User:Toomai/MvM strategy overhaul

I think Community Mann vs. Machine strategy could do with a split into "strats for players" and "strats against bots". This'll be the former.

Colours for reference (from paint, like mission tables):

Essential	The average MvM player will expect to see this in their teammates' loadout, and for good reason.
Recommended	A generally-preferred option that nevertheless has some weaknesses.
Average	Has pros and cons, or might simply have an underdeveloped meta.
Discouraged	A pro could probably make this work, but there are better options.
Worthless	For whatever reason, this has no practical use in the mode.

All-class strategy

• Teamwork is more vital than ever. Make sure to communicate at all times.
• No matter how many robots you kill, they won't drop any sources of ammo. Take note of ammo and Dispenser locations for when your supply runs low. You will still find drops should a teammate die, so make sure it doesn't go to waste. You can also resupply from destroyed building parts, most commonly if a Sentry Buster has just came through, but first make sure that the Engineer is not trying to collect them so he can rebuild.
• Robots are incapable of jumping unless specifically designed to do so. If robots are chasing you, evade them by jumping on or over something.
• The 100-credit bonus for collecting all the money in a wave is easily a game-changer. Do whatever you can to get all the cash, and keep communicating with the team to ensure nothing gets left behind.
• Consider your loadout very carefully before the first wave begins. Once the first wave is completed, you have to wait quite a while until the one and only refund is available. Switching weapons or classes without using the refund, and therefore having less money available for upgrades, is an advanced tactic and should not be attempted by beginners.
• Before each wave begins, take note of the holographic arrows that show the preferred path of the bomb. While some robots will be programmed to flank, the bomb carriers will attempt to follow this path as best as possible, and so should be where the bulk of the team's defenses should be set.
  • Robots may stray from the intended path to chase down a player and stay off the path afterwards. Keep an eye out for stragglers.
  • If the bomb is pushed too far off the intended path and the carrier is killed, future carriers may decide to break from it and take the new shortest route. Classes with knockback should be careful about causing this.
  • Once the bomb reaches the alarm zone at the end of the map, robots will no longer care about sticking to the intended path, and will come from all sides.
• Watch out for melee robots. Even though robots can't get random crits, melee attacks cannot be resisted, which will cut your health down faster then you might expect. Do not try to out-melee robots unless your class is specifically built to do so.
• Players have time before the robots enter the playing area to mobilize according to what they are and where they're moving. Time your explosives correctly to hit them just as they begin to fight - too early, and they will take no damage.
• Keep your team's composition balanced. Your team should have enough of a mix of bullets and explosives, of crowd control and raw damage, that no one wave can completely stymie everyone.

 Scout

General

• Scouts have a large credit-collection radius and gain health from collecting cash, making them the most popular choice for the team's dedicated banker. As long as his teammates are killing robots, a Scout can forego pure damage and simply get money, helping himself stay alive while helping ensure the team can afford the most upgrades. Scouts focused on money should be aware of where all the robots are at all times, moving around the field at high speed to avoid missing any money that lone stragglers might leave behind.
  • Make sure to stand near or on a tank that is about to be destroyed. The riches that it contains will give you a ridiculous health boost.
• Scouts aren't exactly slouches in the damage department. While they don't fare well against large hoardes, they excel at dealing high damage to giants and tanks while simultaneously keeping the robots' attention off his teammates. A good Scout knows how to contribute to robot-killing without ignoring money.
• With the ability to skip the respawn timer, Scouts can often afford to take risks. Even without a Teleporter, he can go for dangerously-placed money piles or pick off protected Medics with less risk than other classes.
• If you have a Sniper on your team, pay attention to any red money he creates via headshots. While it still grants you overheal, it's technically already collected, meaning you don't have to run over and collect it if something more important demands attention.
• Some Scout players prefer to switch to a different class and utilize their refund before the final wave of a mission, under the logic that money is less important and another class such as Heavy may fare better against the final wave's robots.

Loadout

Primary
Scattergun	You can never go wrong with the stock Scattergun.
Force-A-Nature	Cheaper to upgrade to reach higher damage potential, and knockback is helpful to control robots, but your teammates may not appreciate it if you make robots bounce around every time you shoot them.
Shortstop	Effective at longer ranges and has good maximum damage rate, but is more expensive to upgrade.
Soda Popper	Cheaper to upgrade to reach higher damage potential and also unlocks additional mobility through Hype.
Baby Face's Blaster	Against hordes of robots, it becomes quite easy to build the weapon's Boost meter and keep it full even after taking damage. However, it has the lowest damage potential of all the Scout's primaries, and upgrading movement speed already brings the Scout to near the game's running speed cap.
Back Scatter	Being able to mini-crit giants from behind can be useful, but there are several better ways to achieve mini-crits, and the weapon is otherwise outclassed by the other options.
Secondary
Pistols	In essentially all situations, it is more effective to simply reload the Scout's primary weapon than to switch to his less-damaging secondary one, especially once reload speed has been upgraded. Using a pistol for its higher long-range damage is also simply subpar, as it's not worth upgrading.
Bonk! Atomic Punch	The invincibility that Bonk! provides makes it possible to collect dangerously-placed credits safely, but it is generally inferior to Über Canteens, as it renders the Scout unable to attack for a sizeable amount of time.
Crit-a-Cola	The extra damage provided by Crit-a-Cola is not a bad option for a purely-offensive Scout. Compared to the Fan O'War, it can deal mini-crits to several enemies at once, but cannot do so for teammates.
Mad Milk	Mad Milk is an exceptional team support tool, allowing teammates to heal by attacking sodden enemies, and a single inexpensive upgrade makes bots easier to hit and cripples Giant Scouts' ability to tear through the team's defenses.
Flying Guillotine	Designed to destroy singled-out, stunned targets, the Flying Guillotine has poor utility against a horde of robots.
Melee
Stock	The Bat and Holy Mackerel do not have any positive attributes to take advantage of, making them unsuitable for MvM compared to the alternatives.
Sandman	The ability to mark giants for death at long range is useful, but the upgrade required to do so is expensive, in addition to requiring ammo. The Sandman also reduces the Scout's max health significantly, which while not much of an issue after collecting a lot of credits, will be a concern at the start of each wave.
Boston Basher	While there is minor utility in helping your Medic build ÜberCharge or revealing Spies, time spent smacking robots to make them bleed would be better spent simply killing them with your primary weapon.
Candy Cane	A good Scout should be overhealed at all times from collecting credits, and the health kits that drop from killed robots will be in the line of fire more often than not, making them risky for teammates to go for. The Candy Cane is a good source of afterburn control if there are a lot of enemy Pyros, but the substantial increase in explosive damage is costly.
Sun-on-a-Stick	The Scout has higher damage-per-second with non-upgraded primary weapons than using this weapon on burning enemies. Its only potential use is against Heavies with the Fists of Steel, and even then this requires a Pyro on the team.
Fan O'War	One hit from this weapon marks giant robots for mini-crits for 7.5 seconds, effectively cutting their maximum health by 25% if it is constantly re-applied. With no upgrades required, it is one of the most effective ways to accelerate the takedown of stubborn robots.
Atomizer	A single extra jump is negligible in the grand scheme of things, especially if the Scout has the Soda Popper or jump height upgrades.
Wrap Assassin	Bleeding is a generally ineffective means of damage, and the weapon is basically incapable of killing enemies straight-up, making it a poor choice overall.

Upgrades

Personal
Resistances	It is important for a Scout to shrug off damage before he can get his health supercharged by money at the start of waves, and it is even more useful to maintain such overheal levels.
Mobility	Movement speed and jump height are useful to not only dodge enemy fire, but get around the map to collect all the credits. It is potentially overkill to maximize these upgrades, as moving too fast or jumping too high can make it difficult to actually attack enemies.
Regeneration	This upgrade has no use for a Scout that remains at full health or above by collecting credits, which he should be doing.
Primary
Damage output	Upping damage dealt helps immensely with killing Medics in one shot and destroying Tanks.
Penetration	Since the Scout's primary weapons deal the most damage at point-blank, robot crowds must be extremely thick to get much more than chip damage beyond the frontmost target. Situational as a result.
Ammo	One of the Scout's main weaknesses is an inability to keep fights sustained due to lacking clip and ammo. Upgrading these attributes plus reload speed makes him even more of a damage-dealer.
Health on kill	Scouts effectively already have health-on-kill via credits, so it's a bit of a waste to upgrade.
Secondary
Pistols	Even for Scouts that are using a pistol, quite a lot of money must be spent here for any notable effect.
Bonk!	If you're going with a soda can, this is all that's available, so might as well use it.
Mad Milk	The snaring effect of upgraded Mad Milk is cheap and powerful. Recharge speed can be help but is less necessary.
Melee
Offensive	Scouts generally should not be using melee weapons on robots as a killing tactic.
Projectile	If a Scout has indeed chosen to use the Sandman, these upgrades are highly useful.
Canteen
Über	A few seconds of invincibility can give a Scout just enough time to take down a robot and heal from the money it drops, wade through heavy fire to collect credits in a dangerous spot, or simply distract enemies to buy time for teammates.
Kritz	Scouts are already exceptional at killing Tanks, and having crits multiplies his effectiveness even further. It also makes it safer for him to go after Medics, making it easier to kill them in one shot and avoid having them use their charge.
Ammo	Most Scouts should have enough time while they're reloading or between sub-waves to dash to an ammo pick-up or the team's Dispenser.
Return	If a Giant Scout slips through the defense, having a Scout teleport back may be the team's best chance of catching them quickly. However, this is rather situational, and a Scout should be able to catch any other loose robot on his own.

 Soldier

General

• Finding the right range to fight from can be tricky. Too close, and the robots will have an easier time hitting you; too far, and you won't be dealing all that much damage. Fighting from above is always a good idea.
• Be very careful about shooting at or even near Pyros, as they might reflect your upgraded rockets back towards your team.

Loadout

Primary
Rocket Launcher	You can never go wrong with the stock Rocket Launcher.
Direct Hit	Giant robots and tanks are easy targets for the Direct Hit's higher damage, but they cannot be juggled, and splash damage is very important to take out several robots at once.
Black Box	The loss of one rocket is not hard to compensate for with upgrades, and any source of healing is welcome.
Rocket Jumper	For obvious reasons, this item should not be used.
Liberty Launcher	The Libery Launcher's lower damage output is a major problem that is not truly compensated for by its upsides; a stock rocket launcher's 360 damage per four rockets is still higher than the 337.5 of this weapon's five rockets.
Cow Mangler 5000	With infinite ammo, the Cow Mangler is cheaper to upgrade than other rocket launchers. However, the lack of critical hits is a significant downside that the entire team may have to compensate for.
Original	Most MvM maps prioritize height advantage over peeking around corners, so this weapon is not much different than the stock.
Beggar's Bazooka	With a horde of robots to fire at, this weapon's primary downside is negated - there's so much stuff to hit that only distant Snipers will result in missing. With upgraded reload speed, the Soldier can fire single rockets at high speed, or quickly load up a barrage to fire all at once just after activating a Kritz canteen. However, the weapon's smaller explosion radius can be a problem against thinner groups of robots.
Air Strike	Poor in early-game with its reduced splash and damage, but in late-game, raining 16-rocket barrages from above can be devastating.
Secondary
Shotguns	Carrying a sidearm, which really only has a use when out of rockets, is simply inferior to carrying a team-boosting banner.
Boots	These items have no value when defending against an invading robot horde.
Buff Banner	Deploying mini-crits to anyone nearby is an invaluable tool in a mode based on dealing high amounts of damage. Use the banner as often as possible as opposed to saving it for specific moments, to increase the number of times it gets deployed.
Battalion's Backup	Depending on team composition and the presence of crit-boosted robots, this banner can be a better choice than the Buff Banner.
Concheror	Being able to keep the whole team healed is a decent ability, and the mobility boost helps positioning and money collection.
Righteous Bison	The Bison is cheap to upgrade and naturally penetrates through unlimited numbers of robots, but it is difficult to recommend over a team-boosting banner.
B.A.S.E. Jumper	Only really useful in conjunction with the Air Strike, and even then it deprives the player of a team support tool.
Melee
Shovel	The Soldier has far better melee weapons to choose from.
Equalizer	A weakened Soldier will be doing high damage with each melee swing, but this is naturally risky.
Pain Train	With no points to capture, this weapon has no upside.
Half-Zatoichi	As long as the Soldier can land the last hit on an enemy, this will refill his health in an instant, making it a decent choice when surrounded.
Disciplinary Action	Aside from its speed-boosting ability, the weapon's ridiculous melee range helps in attacking Steel Gauntlets at a safe distance.
Market Gardener	In a mode with many foes at once, taking out one at a time with a rocket jump in between is very inefficient.
Escape Plan	A good retreating tool, though crit resistance might need to be applied for best usage.

Upgrades

Personal
Resistances	Blast resistance reduces damage taken from rocket jumping, making it a good choice even for Soldiers that are otherwise not investing in resistances.
Mobility	Rocket jumping mostly overshadows any usage that mobility upgrades can provide.
Regeneration	The health loss from rocket jumping, fall damage, and close-range fighting can add up quickly. Having free health regeneration can help offset this quite well.
Primary
Rocket specialist	Most Soldiers should try to put at least one point into this upgrade, as it will allow direct hits to override distance falloff (which is especially useful on tanks) in addition to stunning the target. Soldiers may or may not want to buy any more depending on how well they can tolerate the rocket speed modification.
Damage output	High damage output is the Soldier's main job, and will help charge his banner faster.
Ammo	Reload and firing speed are the most important upgrades to buy, as they offset the Soldier's arguably-main weakness. Ammo capacity is less universally-helpful but still very useful.
Health on kill	Soldiers should be racking up a lot of cleanup kills, so this is not a bad idea to get.
Secondary
Sidearms	Even for Soldiers that are using a shotgun or the Bison, quite a lot of money must be spent here for any notable effect.
Banners	It is usually more efficient to have longer-lasting buffs as opposed to building, using, and rebuilding multiple shorter buffs.
Melee
	Soldiers who wish to get health from killing robots should probably be using the Half-Zatoichi as opposed to buying the related upgrade, and melee attack speed only really has a use when fresh out of rockets.
Canteen
Über	There's nothing wrong with temporary invincibiliy, but most of the time a Soldier can simply rocket jump away from bad situations.
Kritz	Crit rockets are a Soldier's best weapon in MvM. Use them liberally.
Ammo	There is situational use in an instant clip refill.
Return	Soldiers should be capable of catching up to bots without teleporting.

 Pyro

General

• Pyro is a challenging class to start with, as there's usually not enough money to start a mission to fully invest in what he needs to stay alive. Use cover and ambushes to take robots by surprise as opposed to simply running at them.
• With tanks resisting miniguns, Pyros become one of the strongest tank-killers available. Focus on them when possible.
• Use the compression blast wisely. It can be a huge help to set back the bomb carrier or stall fast-moving robots, but don't interfere with teammates that wish to keep robots in a predictable mass.

Loadout

Primary
Flame Thrower	You can never go wrong with the stock flamethrower.
Backburner	Crits from behind are devastating to giant robots, which take a while to turn around, but the costlier airblast will have to be compensated for by either more ammo upgrades or a teammate.
Degreaser	The typical MvM Pyro should be in the fray at all times without need to switch weapons quickly, and while not as bad as the Backburner, its airblast is still more expensive than usual. Afterburn in MvM is almost useless anyway, so reducing it isn't a real downside.
Phlogistinator	With so many robots to burn, a Phlog Pyro should have crits and healing on demand at almost all times. However, the inability to airblast cannot be overstated.
Secondary
Shotguns	Only if a Pyro runs out of ammo would he ever need to switch to a shotgun, a situation that he shouldn't be getting into anyways.
Flare Gun	Shooting flares at Snipers is a decent way of distracting them, or outright killing them if they remain still for a second shot. It is also good for dealing damage to Giants while walking up to them.
Detonator	Similar to the Flare Gun, though with less damage and more mobility.
Manmelter	Gaining crits via extinguishing teammates is very situational, and other flare secondaries tend to result in more damage for less effort.
Scorch Shot	Acts like a long-range airblast to knock back distant robots, but with not much else.
Melee
Fire Axe	The Pyro has far better melee weapons to choose from.
Axtinguisher	Against burning targets, this weapon can deal 131 damage per second. At close range, a flamethrower without upgrades deals 157.5 damage per second. Even against enemies that resist fire damage, this weapon takes so long to deploy that the Pyro should instead choose something that doesn't need simultaneous afterburn to deal high damage.
Homewrecker	Worthless against robots, but gets rid of enemy Sappers, which can be a lifesaver if the Engineer is killed before he can unsap his buildings.
Powerjack	Extra speed to get into close range is helpful, but the damage vulnerability while held negates the minor health boost it provides upon actually landing the final hit on an enemy.
Back Scratcher	In early waves, getting additional health from health packs can be a major source of survival, and even once health-based upgrades and resistances are bought, it still does additional damage. However, the team's Medic and Dispenser become near-worthless to you.
Sharpened Volcano Fragment	With afterburn being unreliable overall, the weapon's lower damage doesn't really jive with the Pyro's playstyle.
Third Degree	While this weapon can eradicate all the Medics off a giant with a single crit swing, it needs three non-crit swings to do so, the second one probably causing them to pop their charge.
Neon Annihilator	There are better ways to kill enemies than to depend on a teammate to soak them.

Upgrades

Personal
Resistances	As Pyros should be spending all their time in close range, being able to resist most of the damage coming their way is essential to remain alive.
Mobility	It is important for a Pyro to get into close range to attack yet also get out if things get to dangerous.
Regeneration	It is difficult to say whether health regeneration is good for Pyros - any source of health is appreciated, and depending on team composition and skill the Pyro might be dealing lots of damage without actually scoring many kills, but regeneration only works of the player is not overhealed from a Medic or health-on-kill.
Primary
Raw damage	Pure damage is the Pyro's main goal, especially against Tanks.
Afterburn	Fully-upgraded afterburn can do a maximum of 240 damage after a total of 20 seconds. This sounds high, but a Pyro can use money on raw damage instead to reach over 300 damage per second and have some cash left over. Afterburn upgrades are simply not worth the cost.
Ammo	For Pyros that don't want to have to leave the fight to forage for ammo, and especially for Backburners trying to airblast robots, this is very useful.
Health on kill	Pyros in the fray should be collecting a lot of cleanup kills, so using them to keep health high is super-helpful.
Airblast force	The majority of robots are easy enough to push around with no money invested here, and the majority of giants have too much knockback resistance for this to matter. Its main use is to throw robots into a setback ditch or deathpit with fewer airblasts necessary, making this almost act like an ammo upgrade.
Secondary
Shotguns	Why are you using a shotgun again?
Flare guns	Pyros should not be spending enough time at long range for these upgrades to matter.
Melee
	Some of the Pyro's weapons can benefit from faster swing speed, but overall the money is probably better spent elsewhere.
Canteen
Über	As Pyros thrive in close range, invincibility is a major boon for when things go south.
Kritz	Not a bad option for destroying Tanks and giants.
Ammo	Pyros that don't wish to leave the fight to find ammo may opt for this.
Return	The ability to catch up to a robot and airblast them back makes Pyro one of the better users of this canteen.

 Demoman

General

• Set massive sticky traps where the robots first become vulnerable to deal insane damage. Tanks are particularily susceptible to this.
  • Be very careful to not set off your stickies too early. If the robots are still invulnerable when they go off, they could fly in any direction across the entire map.
  • If your team has a Medic with the Kritzkrieg, ask him to kritz you before the wave begins so you can lay down a critical sticky trap. It's basically free to do, with Medics having super-fast charge rate between waves. However, this is mostly only effective if the target powerful robots appear early in the wave. Weak common robots would be easy to kill anyway, and a Demoman saving the critical stickies for a giant will often lead to either the team getting pushed back so far that he cannot focus on the robot spawn where he laid them, or his death and loss of his stickies.
• Even during waves, sticky traps are powerful tools for killing Medics before they can use whatever their charge is. If not using stickies as a direct damage tool, try to keep traps active at all times.
• Once the proper upgrades have been bought, Demoknights are quite effective against masses of robots while being comparably ineffective against giants and tanks. Ensure that your team doesn't need extra power against large targets before committing yourself.

Loadout

Primary
Grenade Launcher	You can never go wrong with the stock Grenade Launcher.
Loch-n-Load	Optimized for busting buildings, this weapon has no true advantage against robots, with its various disadvantages rendering it suboptimal for crowd control.
Ali Baba's Wee Booties	Demoknights, or Demomen exclusively focused on their stickies, can find reason to give up grenades for a substantial health boost.
Loose Cannon	The knockback of cannonballs is good for controlling robots' movements, but the weapon deals less damage overall, especially to tanks.
B.A.S.E. Jumper	Unlike the Solider, the Demoman has little reason to hang vulnerable in the sky for long periods of time.
Iron Bomber	Lower explosive radius without a real upside leaves this weapon in a poor spot.
Secondary
Stickybomb Launcher	You can never go wrong with the stock Stickybomb Launcher.
Chargin' Targe	The preferred Demoknight shield, as it has the best resistances, and having Crits On Kill for melee weapons is more effective than charging.
Scottish Resistance	The slower arm time is mostly irrelevant given the robots' predictable movement, and having 6 more stickies active at a time that can be detonated individually grants much more power to sticky traps.
Sticky Jumper	For obvious reasons, this weapon should not be used.
Splendid Screen	Shield bashes, this weapon's speciality, are extremely inefficient at damaging robots.
Tide Turner	Demoknights do not need to charge that often in MvM, and the weapon's weaknesses of "damage shortens charges" and "mini-crit swings only" can be crippling.
Quickiebomb Launcher	The lack of sticky traps is not quite made up for by stronger straight-up damage capabilities.
Melee
Bottle	The Bottle has no upsides to exploit or downsides to tolerate.
Eyelander	While a Demoman with the Eyelander is weaker to start, after a few melee kills, he has much improved speed and health. It works well for any Demoknight, while for a Demoman with stickies, it is riskier.
Pain Train	With no points to capture, this weapon has no upside.
Scotsman's Skullcutter	Having longer range with more damage is countered by slower movement speed. For Demos that are not intending to fight at close range much, this is a good choice for when Steel Gauntlets appear.
Ullapool Caber	With no resupply cabinets in MvM maps, this weapon's one-shot nature makes it very difficult to recommend.
Claidheamh Mòr	While an innate health-on-kill bonus is nice, its damage vulnerability is counterproductive, especially for full Demoknights with nothing else to switch to.
Half-Zatoichi	On a Demoknight with no other weapons to switch to, this can easily make him extremely bulky.
Persian Persuader	While charges aren't as useful as in other game modes, having one available for escape can be useful. Non-Demoknights should never use this, as ammo is scarce enough in most MvM maps.

Upgrades

Personal
Resistances	Even if a Demoman isn't investing too much into resistances, explosive resistance makes sticky jumping and close-range detonations safer. Resistances in general are highly useful for Demoknights, stacking with whatever their shield has.
Mobility	Demoman has slightly below-average mobility with no real need to move around quickly, while Demoknights have shield charges available. Therefore, upgrading mobility is not essential.
Regeneration	Having a way to offset self-damage taken is a strong reason to buy this.
Primary
Raw damage	The higher cost for less effect on both the Demo's explosive weapon slots makes it prohibitively expensive to upgrade both weapons at once. Demos focused on grenades may find upgrading direct damage to be not worth the cost compared to other attributes.
Speed and ammo	If grenades are the weapon of choice, all these upgrades are highly useful.
Projectile speed	While this effectively increases the range of grenades, it can easily throw off players' aim and has no additional properties like the Soldier's version.
Health on kill	Any way of restoring health is welcome, though depending on your loadout and the team you may find yourself dealing a lot of damage without a lot of kills.
Secondary
Raw damage	The higher cost for less effect on both the Demo's explosive weapon slots makes it prohibitively expensive to upgrade both weapons at once. Demos focused on stickies can use higher damage to spread their traps farther out for equal damage, or keep them concentrated for even more damage on fewer targets.
Speed and ammo	If stickies are the weapon of choice, all these upgrades are highly useful.
Health on kill	Depending on your weapon and playstyle, kills with stickies may be either common enough for this to be worthwhile or rare enough that this is not helpful.
Demoknight	Charging more often is more of a bonus than a necessary skill to have in MvM. Taking reduced knockback is a highly-situational upgrade that may not see any use when not facing dedicated pusher robots.
Melee
Demoman	It will probably be more effective overall for a Demoman to invest in explosive resistance and just blow things up at short range rather than switch to his weaker melee weapon.
Demoknight	This is where a Demoknight should be spending most of his money, allowing him to get a single kill with a shield charge and go on a rapid-fire rampage of chained critical sword swings, overhealing him the whole time.
Canteen
Über	There's nothing wrong with temporary invincibility, especially when trying to fight at close range.
Kritz	Crit explosives are immensely useful in MvM, and if the team doesn't have a Medic, this is the best way at using them.
Ammo	There is situational use in an instant clip refill.
Return	Being able to teleport ahead of a slippery bot and lay down a sticky carpet for it is probably one of the better usages of this canteen.

 Heavy

General

• Even with the most health of any class, an unupgraded Heavy is no match for the robot hoarde. With his large size and slow speed, he needs to buy the correct upgrades or receive team support to both stay alive and deal damage.
• Tanks resist 75% of minigun damage. If another threat is present, focus on it instead.
• Due to his low speed, Heavy is arguably the worst class to try and collect credits with, as he will likely be left out of position by the time the next group of robots arrives. Tell your faster teammates where uncollected money lies instead.

Loadout

Primary
Minigun	You can never go wrong with Sasha.
Natascha	More ammo to spare, damage resistance while revved, and the ability to slow enemies while damaging them are extremely useful in certain waves, especially against Giant Scouts. However, the lower damage is quite noticable on already-slow robots.
Brass Beast	While this weapon's extremely high mobility cost can be a major issue if Snipers are present, its natural damage resistance and higher damage output make it a very appealing choice.
Tomislav	The Tomislav's slower firing rate adds up quickly, and robots do not hear deployed miniguns anyway. The weapon's tighter spread is a wash, working well against single targets but holding it back against large swarms.
Huo-Long Heater	Minigun ammo can already be a problem for Heavies, and since afterburn is weak overall, cannot be upgraded, and Spies are both rare and announced, there is not much upside to this weapon.
Secondary
Shotguns	Most of a Heavy's time and money should be spent on his minigun; switching to a shotgun is not really any faster than spinning up, and there are better ways to deal with ammo issues.
Sandvich	Providing a free medium healthkit to teammates and a full heal to himself with unoccupied, the Sandvich is highly useful even if the team has a Medic.
Dalokohs Bar	For best effectiveness of this item, the Heavy has to munch on it multiple times a minute, taking a lot of time away from participating in the battle. It is also weaker than his other lunchbox items at healing teammates, acting as only a small health kit. But the real problem with this item is that simply having a Medic (or other means of overheal) renders it completely ineffective.
Buffalo Steak Sandvich	The Heavy's main draw in MvM is his minigun; he should not be putting it away to punch robots while taking increased damage.
Melee
Fists	Pow!
Killing Gloves of Boxing	It is usually quite risky for a Heavy to try and land a finishing punch on an enemy, but being able to do so effectively grants him a free Kritz Canteen. Best used with a minigun of stock or reduced spin-up time.
Gloves of Running Urgently	As Heavies generally should not be getting into melee combat, the GRU's running speed boost is a good way to help him move about the field. Upgrading crit resistance helps offset the only remaining downside.
Warrior's Spirit	Increasing damage taken while encouraging melee combat is not a promising combination, as unless his enemies are oblivious, the Heavy is almost certain to take more damage than the item can heal.
Fists of Steel	Steel Gauntlets use this item because their goal is to stay alive, not to kill enemies. As the Heavy himself is in somewhat of the reverse situation, he finds less use for it.
Eviction Notice	By far the Heavy's weakest melee option, but provides a decent speed boost while taking less (and non-mini-crit) damage than the similar G.R.U.
Holiday Punch	Robots contain (repaired) Humor Supression Pumps. Attempting to get them to laugh is futile.

Upgrades

Personal
Resistances	Even though he has high health, being a big and slow-moving target means that damage resistances will be much welcomed.
Mobility	Upgrading movement speed fixes one of the Heavy's biggest weaknesses. Jump height is much less useful but allows him to get more distance out of the jump-around-corner-and-fire strategy.
Regeneration	With the Heavy's high max health, it can take a while for this upgrade to reach good usefulness.
Primary
Destroy projectiles	With both points invested into this upgrade, enemy robots will find it quite difficult to get projectiles through the Heavy's wall of bullets. While expensive, it is the team's most reliable way of dealing with projectiles, as it doesn't interfere with the Heavy's damage output.
Knockback rage	The usefulness of this upgrade depends on a large number of factors, as activating its knockback comes at the expense of damage. It is best used when the Heavy doesn't think he can kill a particular robot before it gets away.
Penetration	Piercing bullets multiplies a Heavy's damage output when firing into crowds by a large factor - which is why he's the only class for which this upgrade is both expensive and restricted to 4 enemies per bullet at max level.
Ammo	Heavies need lots of ammo, especially once firing speed is upgraded. However, this upgrade is less necessary if the team has a generously-placed Dispenser.
Firing speed	The only way to upgrade a minigun's damage output, at the cost of more ammo per second. It also makes it easier to take out projectiles.
Health on kill	While it's certainly a useful upgrade, with so much money being needed elsewhere, it's unlikely to end up being used much.
Secondary
Shotguns	The Heavy's power is in his minigun. Upgrading his shotgun is typically a waste of money.
Food	It wouldn't hurt in theory, but throwing Sandviches slightly more often means less time spent unloading bullets.
Melee
	Heavies at close range should be dumping lead into robots, not punching them. That said, there is merit in using these upgrades to aid a K.G.B. spree, though this cannot reach the effectiveness of a Demoknight.
Canteen
Über	A burst of guaranteed survival is quite a useful tool for Heavies.
Kritz	Having crits on demand is a powerful tool.
Ammo	Ammo can be a problem for Heavies, so having an instant refill is very useful.
Return	With the slowest running speed and the need to spin up his minigun, it's impractical at best for a Heavy to be the one chasing down stragglers.

 Engineer

General

• Buildings placed during setup time cost no metal and are automatically fully upgraded. If you happen to join the server late before a wave begins, make sure you at least construct all your buildings before setup time expires.
• Buildings being hauled don't reduce your speed and are operational instantly on redeployment. Don't be afraid to move things around if the bomb gets through your first line of defense.
• Most robots are blocked by your buildings. Place Sentry Guns at chokepoints, narrow passages, or corners so that fast-moving robots cannot squeak through.
• Sentry Busters are inevitable. Always have a plan for when they appear, whether it be taking your Sentry away from their explosion, or luring them to a specific location.
• With fewer sources of ammo than other modes, Dispensers are critical for keeping teammates' ammo restocked. Try to place them in locations that everyone can reach quickly (including you), without being exposed enough for robots to target it.
• Teleporters are critical for getting recently-respawned teammates back into the fight. Keep the exit away from your Sentry, so it's not at risk from Sentry Busters.
  • Teleporters can also be useful as makeshift elevators, letting teammates skip time-consuming and/or dangerous portions of the map to gain height advantage. Place the entrance where allies are likely to take cover, and place the exit at a good vantage point that is not easily accessible otherwise.

Loadout

Primary
Shotgun	You can never go wrong with the stock Shotgun.
Frontier Justice	With the amount of kills and assists the typical Engineer should be racking up, the Frontier Justice is a source of almost limitless crits once the first Sentry is destroyed. Engineers with this weapon should prioritize staying alive and make sure to destroy their Sentry between waves (or even allow Sentry Busters to do so during waves) to unlock the crits.
Widowmaker	Since it uses Metal for ammo and needs no reloading, the Widowmaker is very cheap to upgrade, and in the hands of a decent shot will keep you constantly filled with Metal. With piercing bullets and max metal/metal regen upgrades, the weapon can become a source of unlimited harrassment and distraction.
Pomson 6000	While not very useful against most robots, the Pomson excels at weakening Medics and Spies, giving the team a wider window of opportunity to destroy them.
Rescue Ranger	The ability to heal and haul buildings at long range less Engineers place high-level Sentries as distractions and cart them off to safe havens when their health gets low, or quickly teleport them back and forth across an area. However, as Engineers do not run slower while hauling in MvM, it is not as useful for moving up a base as in other modes, and being marked for death can be a serious problem if your nest is swarmed.
Panic Attack	It is risky for an Engineer to rely on this weapon, as he cannot switch weapons while loading or firing it, which can leave his buildings open if he can't switch back to his wrench in time.
Secondary
Pistol	While there's nothing inherently wrong with the Pistol, it is simply outclassed by the Engineer's other options unless he is going full Gunslinger.
Wrangler	The Wrangler allows Engineers to intelligently prioritize targets, raise their Sentry's DPS for taking down giants and tanks, absorb tons of damage when combined with building health upgrades, and fire back at distant Snipers or Spies. However, it does have downsides; activating it chews through Metal even faster, can allow Scouts to slip though the front lines, and hampers repairs. Even if not used much, simply having it equipped for a few specific situations can mean the difference between success and failure.
Short Circuit	The ability to wipe out entire volleys of projectiles is very powerful, but at a steep Metal cost that cannot be easily replenished without switching away from the weapon. In addition, Heavies and Medics have more effective tools for projectile control, even though they have to buy them.
Melee
Wrench	You can never go wrong with the stock Wrench.
Gunslinger	Mini-Sentries are cheap and fast, the health boost allows the Engineer to dive into the fight himself more, and punching crits can be effective against giants. However, giving up level 3 sentries is not a choice to be made lightly, and the team will need to prepare itself accordingly before the first wave begins.
Southern Hospitality	Engineers should not be attacking robots directly with their wrench outside a last resort, meaning this weapon has no upside.
Jag	The Jag is a good choice for Engineers that wish to forego upgrade canteens, but the extra difficulty repairing buildings may result in rebuilds more often.
Eureka Effect	While this somewhat gives an Engineer an infinite supply of Return canteens, its metal-collection penalty can cripple an Engineer's ability to keep his buildings operational, requiring upgrades to metal reserves to keep pace. In addition, the process of using its teleport is quite long, making it hard to use when under fire or time is of the essence. As long as the player keeps upgrade canteens stocked, the weapon's construction boost penalty is irrelevant.

Upgrades

Personal
Resistances	It can help to be shielded from incoming fire directed at your Sentry, but resistances are otherwise of less use for Engineers than most other classes.
Mobility	It's always nice to reach buildings faster in order to repair them, or more easily direct Sentry Busters to specific locations.
Regeneration	These upgrades allow an Engineer to place his Dispenser where the team needs it more than himself. Of the two, Metal regen is more important, as unlike health, Dispensers have a limited supply of it.
Primary
	Most of these upgrades are of situational use, if only because Engineers should be spending their money elsewhere. However, the Widowmaker in particular is very cheap to upgrade as it has no clip size, no reload, and no independent ammo source.
Secondary
Pistol	Unless the Engineer is going full Gunsligner, he shouldn't be spending any money here.
Short Circuit	As the only upgrade available for the Short Circuit, it's not a bad idea to use if you find yourself with too much Metal.
Melee
Swing speed	This upgrade allows an Engineer to work on his buildings faster, which is pretty much always a good thing.
Health on kill	Unfortunately, because of how Engineers will probably have max crit rate at all times due to dealing high damage, upgrading this costs double the cash as any other class (just like Spy). This alone makes it less appealing to use, as it should only manifest itself if the nest is swarmed.
Buildings
Disposable sentry	Many players consider this a "trap" upgrade, costing a lost of money for a very minor benefit. However, it can be useful in certain situations by acting as a distraction from behind the robots' path, and while it's not affected by upgrades it still contributes revenge crits. Engineers should not buy this if they don't plan on keeping it up at all times.
Health	Sentries will have a lot of damage aimed at them at all times, and this upgrade is one of only two ways to migitate it (the other being to activate the Wrangler). It also doesn't hurt to make front-lines Dispensers more resilient.
Firing speed	A double-edged sword; higher damage-per-second is offset by faster ammo depletion and Metal usage, which in turn requires further upgrades to keep up.
Two-way teleporters	Acting as a free return canteen for the whole team, a well-placed two-way teleporter can also let the team jut back to base for more upgrades mid-wave or even let them fight on two fronts. However, these kinds of strategies only work if the entire team is on the same page.
Max metal capacity	Even a single level of this upgrade is enough to lay down both a Sentry and a Dispenser and then fire a Buildings Upgrade canteen, planting a nest from scratch in two seconds flat. Further upgrades supplement the Widowmaker, Short Circuit, and just building maintenance in general.
Dispenser range	Ridiculously cheap for the utility it provides, for example allowing a Heavy to lay down fire from the middle of a corridor while being resupplied by a Dispenser out of sight around the corner.
Canteen
Über	There are better ways of dealing with Sentry Busters than by Übering the Engineer and Sentry.
Kritz	Additional Sentry firing speed is probably better off left to the Wrangler than a canteen.
Ammo	An instant Metal refill can be a lifesaver in some situations, especially in conjunction with the Widowmaker or Short Circuit.
Return	Being able to haul a level 3 Sentry to the base in an instant is a useful tool, but often the same thing can be accomplished by building a two-way teleporter.
Buildings	The ability to put up a level 3 Sentry and Dispenser in an instant cannot be understated, especially when there is no time to rebuild manually during a wave. It can also be used to instantly fully heal all existing buildings, though there's risk in pressing the button too late and upgrading a pile of rubble.

 Medic

General

• Revive teammates whenever possible. Even with a Teleporter active, it's the fastest way to get them back into the fight.
  • However, there may be situations where healing an existing teammate to keep them alive may be more beneficial than letting them die and subsequently dragging the revived teammate into a poor position.
  • Activating your ÜberCharge lets you revive much quicker, at the expense of the Über's intended use.

Loadout

Primary
Syringe Gun	The stock Syringe Gun has no upsides to work with or downsides to avoid.
Blutsauger	Unless the Medic is actually fighting with this weapon (and therefore not healing his team as much), he is hampering his self-regeneration with it.
Crusader's Crossbow	With the ability to heal teammates at long range and deal surprisingly high damage to distant Snipers, the Crossbow is quite useful in many situations.
Overdose	A minor damage reduction conbimed with a minor speed increase equals out to an average option.
Secondary
Medi Gun	Invulnerability is a strong tool against the robot horde, allowing a patient (or two) to survive literally anything while spitting out damage. However, out of all the Medic's options, it takes the longest to build up.
Kritzkrieg	As dealing high amounts of damage is the main goal of the mode, having command of guaranteed crits is a godsend to any class it's trained upon. It allows Demos to spread out critical carpets of stickies before the wave begins, Soldiers to fire walls of crit rockets at the oncoming horde, or Pyros to melt the sides off a Tank. It also allows the Medic to spend his money on the cheaper canteens to share.
Quick-Fix	With its higher healing rate, the Quick-Fix can charge its projectile shield and revive teammates faster, and the knockback immuniy its Megaheal provides can help against pusher robots. However, its charge is otherwise quite weak, and its lower overheal can be a problem if not upgraded to compensate.
Vaccinator	When used properly, the Vaccinator can render both the Medic and his team completely immune to crits and almost immune to whatever else is incoming. Its main drawback is the higher learning curve required to tap into its versatility.
Melee
Bonesaw	The stock Bonesaw has no attributes, useful or otherwise.
Ubersaw	It is risky for a Medic to poke a robot with his melee weapon to acquire über, but simply carrying the weapon in case an opportunity presents itself (such as stunned or sapped robots) is never a bad idea.
Vita-Saw	Comapred to regular multiplayer, the balance in MvM of "stay alive" versus "rebuild time after death" is skewed much more heavily towards survival, making the Vita-Saw's max health reduction a much larger disadvantage (especially once charge speed is upgraded).
Amputator	The Medicating Melody and higher regeneration rate are good reason to choose the Amputator, as its downside in damage is not really relevant.
Solemn Vow	All players can see the health of giant robots and Tanks at all times, making the weapon's only upside irrelevant.

Upgrades

Personal
Resistances	As always, staying alive is a priority for Medics. However, money has to be spent elsewhere to keep teammates alive better, so it's difficult to invest here.
Mobility	Medic is already the second-fastest class, but upgrading speed further helps when dodging attacks.
Regeneration	Medics have natural health regeneration already, so upgrading it isn't too useful.
Primary
Syringes	Usually, Medics have no need to be firing syringes at enemies, so upgrading said weapon is of questionable merit. Mad Milk Syringes is a unique attribute, but it's more effective to just heal teammates directly and build über instead.
Crossbow	In terms of upgrades, the Crusader's Crossbow is not much different than other primaries: not much need to upgrade it.
Secondary
Charge speed	This is a good upgrade to get to counter the detrimental effect that overhealed teammates have on building über.
Projectile shield	A fantastic way to migitate incoming damage, with the potential to nullify entire critical barrages.
Charge duration	Increased invulnerability time is a major asset when dealing with robots of high damage output. On the other hand, some players may find themselves wondering what to do with too many crits, and if there's nothing left to kill then the Medic has to wait until the charge runs out before building another one.
Overheal	With no way to upgrade max health, overheal is the only way outside resistances to survive high-damage attacks. Scouts will vastly appreciate their money-infused health not decreasing as fast (especially between waves).
Healing	Faster healing means faster projectile shield charging and faster teammate reviving, while also cutting the time needed to reach max overheal.
Canteen specialist	Even if a Medic has no intent to share his chosen canteen with teammates, there is zero disadvantage to doing so, and as a bonus it makes canteens more effective overall. Note that Medics should always confirm buying this before buying canteens so that the price reduction applies.
Melee
	While attack speed can offset the Ubersaw's only downside, it's hardly worth it in most situations, and Medics shouldn't really be attacking with any other melee weapons.
Canteen
Über	A solid choice for Kritzkrieg users, allowing the Medic to dispense both crits and invincibility.
Kritz	When not using the Kritzkrieg, this lets the Medic pop crits on patients anyway for short bursts of high damage. Even then, having the Kritzkrieg then lets the Medic effectively charge two teammates at once.
Ammo	With proper team communication, a Medic can use an Ammo canteen to double the size of his patient's clip during a Kritzkrieg, Buff Banner, or patient's Kritz canteen. Without proper communication, the patient may buy Ammo canteens of their own or break off their attack preparing to reload. Note that if using this canteen, there is no need to buy the third point of Canteen Specialist, as this canteen cannot be made any more cheaper and has no duration to extend.
Return	Medics cannot share this canteen, so if a robot sneaks through to the base, they will have to take them out alone with weapons that are likely not upgraded.

 Sniper

General

• A Sniper's role is to eliminate high-profile targets, specifically Medics, Snipers, Engineers, and giants (roughly in that order of priority). Target the bomb carrier if necessary, but if you can take out the supporting robots, your team should be able to handle the bomb.
  • Medics in particular should be your primary target, as nonlethal damage to them will cause ÜberCharge deployment. Buying the proper upgrades will make this task simpler.
• Bomb carriers and giants move at slow speeds, and in the case of the former, must stop periodically to taunt. Take your time lining up headshots on them for massive damage.
  • Headshots also allow you to automatically collect whatever cash is dropped by the killed robots in the form of red money.
• Consider letting stray robots be if you aren't confident in your headshotting ability. Killing strays with a bodyshot will drop money in the middle of nowhere, which someone will have to take a long time collecting.
• Snipers are poor at damaging tanks. Shoot them only if you have nothing better to do.

Loadout

Primary
Sniper Rifle	You can never go wrong with the stock Sniper Rifle.
Huntsman	Without explosive headshots, a Huntsman Sniper loses an effective manner of crowd control, which cannot reasonably be made up for with the bleeding upgrade.
Sydney Sleeper	Applying Jarate at long range is a useful tool, but its lack of critical damage on headshots is a major downgrade.
Bazaar Bargain	While this weapon starts with very poor charge rate, after a trivial amount of headshot kills, it charges at triple the base speed. As long as the player can stay alive, this lets him deal out massive damage in short order.
Machina	The downsides of the Machina are minimal compared to its higher damage and built-in penetration when fully charged.
Hitman's Heatmaker	The Heatmaker's Focus ability allows the Sniper to rapid-fire partially charged heatshots, and with so many robots to kill, it is possible to remain scoped almost indefinitely.
Classic	The inability to deal headshot damage when not fully charged is difficult to work around, but being able to do so without being scoped can help keep an eye on other threats.
Secondary
SMG	The SMG's only use is for personal defense when attacked up close.
Jarate	An incredibly useful tool for any team, Jarate not only applies mini-crits to multiple enemies at once, but with a single cheap upgrade, it also slows them down and renders them unable to slip through the team's defenses.
Razorback	With no resupply lockers in MvM maps, and occasional bugs that allow Spy Robots to circumvent the item, the Razorback has very poor situational use.
Darwin's Danger Shield	Extra health and bullet resistance is helpful, but the higher explosive weakness and lack of a secondary weapon make this item less than ideal.
Cozy Camper	Free health regeneration is nice, but the flinching immunity is situational, as robots tend to not fire at Snipers until they are decently close anyway.
Cleaner's Carbine	Snipers that wish to fight on the front lines can find the Carbine a useful source of mini-crits, but this requires him to deal a fair bit of damage, and the weapon's slower firing speed is expensive to offset.
Melee
Kukri	A stock melee weapon with no upsides to exploit or downsides to avoid.
Tribalman's Shiv	A Sniper in melee combat is probably trying to save his own skin rather than trying to go on the offensive against bulky robots, and bleeding is more often than not a poor source of damage.
Bushwacka	With several ways to gain mini-crits, such as Jarate or a teammate's Buff Banner, the Bushwacka's ability to turn them into full crits is exceptionally useful against oblivious giants and tanks. However, merely possessing this weapon makes it much easier to die.
Shahanshah	Using a melee weapon as a Sniper is probably a last resort, so having higher damage when injured is not that bad.

Upgrades

Personal
Resistances	Bullet resistance can help against enemy Snipers, but generally Snipers shouldn't be taking much damage until they're dead already.
Mobility	Snipers typically don't need to get anywhere in a hurry, but there may be a few perches that Spy robots may not be able to reach you.
Regeneration	Naturally healing after getting clipped by a stray shot means a Sniper can remain in his sniping spot and shoot robots, but health-on-kill is more effective if the player is skilled.
Primary
Raw damage	Effectively lowers the amount of charge needed to kill non-giants, while further multiplying the damage dealt to giants.
Penetration	Firing high-powered bodyshots into crowds can take out a lot of lower-health robots at once.
Explosive headshot	The definitive Sniper upgrade, allowing him to unload a single bullet into a giant's head and instantly delete all the Medics healing it, or shoot the slow-moving bomb carrier and wipe out all its surrounding allies. Note that this upgrade activates when shooting a robot in the head while scoped, even if the player's chosen rifle normally doesn't deal critical damage in such situations.
Faster charge	Depending on playstyle, this can be treated as just an alternative to higher raw damage.
Bleed on target	The Huntsman's answer to explosive headshots is underwhelming at best, as bleed damage is only slightly more effective than afterburn.
Ammo	Most sniping spots have ammo available, and unless a Sniper is unloading a ton of shots in rapid succession he shouldn't have much ammo worries.
Reload speed	This upgrade is difficult to quantify, as reloading faster does not allow the Sniper to re-scope any faster. It is however exceptionally useful in conjunction with the Hitman's Heatmaker, due to its ability to remain scoped after firing.
Health on kill	A skilled Sniper can use this to keep himself overhealed at all times, and even a less-skilled one can use it to heal himself without having to move.
Secondary
Sidearms	A lot of money has to be spent here for an SMG to reach "viable" levels. It is better spent elsewhere.
Jarate	The snaring effect of upgraded Jarate is cheap and powerful. Recharge speed can be help but is less necessary.
Melee
	Rasing the Bushwacka's swing speed for tank-killing purposes is about as useful as these upgrades get.
Canteen
Über	Snipers have little use for invincibility unless they are overwhelmed, in which case they probably won't be able to survive regardless.
Kritz	The ability to rapid-fire headshot damage without scoping is good in a pinch.
Ammo	Most Snipers shouldn't be running through ammo fast enough to require refilling while busy, and many sniping spots have ammo pickups available.
Return	If a robot gets through the defense, a Sniper might not be able to do much to stop it even if he heads it off.

 Spy

General

• Unless robots see you apply a disguise or you are on fire, robots will not suspect you as a Spy, even if you bump into them or they see you applying Sappers.
  • Be very careful around Pyros, which might accidentally light you on fire as part of attacking a teammate.
• As far as fooling robots is concerned, choice of disguise is irrelevant. However, do not disguise as a class slower than you are, as this will make it more difficult to catch up to targets.
• Spy is a decent money-gathering class. While he lacks the special abilities of a Scout, his disguise lets him collect credits without coming under fire.
• Use your Sapper wisely. While it can be used to disable a giant robot's entire pack of Medics, slow lightning-fast robots to a crawl, or disable Engineer buildings, you need to be aware of the weapon's cooldown timer and consider saving it for an upcoming greater threat.
• Sapped non-giant robots can be backstabbed from any angle. When you disable a group, take them out as fast as possible.
• It takes robots a few seconds to realize an ally has been stabbed. Land as many stabs as you feel is safe before cloaking, re-disguising, and repeating.
• Chains of backstabs can deal massive damage to giants in short order (once the knife is sufficiently upgraded). Try to predict when the giant will notice your presence and turn around so you can retreat.
• Tanks cannot be sapped or stabbed. Whenever possible, focus on the robots supporting the tank and let your teammates do the main job.

Loadout

Primary
Revolver	You can never go wrong with the stock Revolver.
Ambassador	With less damage and a focus on headshots, no upgrades that take advantage of headshots, and a mantadory cooldown period, the Ambassador is not exceptionally useful against a horde of robots.
L'Etranger	Spies are not expected to contribute ranged damage anyway, so L'Etranger's lower damage is not much of a downside. On the other hand, it allows cloak to be charged faster and used more, allowing the Spy to position himself better.
Enforcer	If a Spy is shooting something, it is probably a Tank, making disguising useless and this weapon a bad choice.
Diamondback	While it does slightly less damage, the ability to store many crits via backstabs allows the Spy to do appreciable damage to faraway enemies and Tanks.
Secondary
Sapper	There is nothing exceptional about the Sapper.
Red-Tape Recorder	There is no functional difference between the two sapper options when used on robots. Against enemy buildings, the Red-Tape Recorder can delevel buildings, but leaves them around for potential saving for longer.
Melee
Knife	You can never go wrong with the stock Knife.
Your Eternal Reward	The specifics of robots' spy-detection mechanics result in this weapon being functionally useless.
Conniver's Kunai	The initial health penalty is a major issue, but the Kunai eliminates the need for health-on-kill upgrades.
Big Earner	With not-as-drastic health reduction, the Big Earner makes it very easy to keep cloak fully charged and allows the Spy to chase down a faster target.
Spy-cicle	Being without a knife, the Spy's primary weapon in MvM, for any length of time is a major drawback that does not quite compensate for its fire immunity.
Watch
Invis Watch	Ammo tends to be scarce on MvM maps, so refilling cloak can be an issue.
Cloak and Dagger	This watch is suited for slow or stationary espionage, which does not jive well with the mode's mechanics.
Dead Ringer	Robots are always completely fooled by feigned deaths unless the Spy catches on fire, and they ignore decloacking noises. As long as the Spy can keep his cloak fully charged, he can use the Dead Ringer to escape from almost any situation and come back for more.

Upgrades

Personal
Resistances	Lowering damage taken lets a Spy take more time getting to his main target if he falls under fire, and staying alive in general is a high priority.
Mobility	Upgrading movement speed is essential to catching fast robots to stab them. Jump height has comparatively little use.
Regeneration	This upgrade's usefulness primarily depends on whether the Spy has health-on-kill for his knife or not. If not, this is an exceptional way to recover health while cloaked and survive longer.
Primary
	Spies should not be using their revolver enough that either of these upgrades activate.
Secondary
Sapper power	Sappers are not really all that effective when not upgraded, making at least one point of this almost essential.
Melee
Armour penetration	187.5 damage per backstab isn't that impressive considering most giants have above 3000 health, meaning Spies should try to maximize this as soon as possible.
Crits on kill	This lets a Spy kill a lone robot and unload several crit revolver shots into a tank or faraway giant. However, depending on how many easy pickings there are, using the Diamondback instead may be more effective overall.
Attack speed	Upgrading swing speed lets a Spy get more stabs in before a giant turns around, which can make a great deal of difference.
Health on kill	Not so hot when a Spy is focusing on giants, but when he's stabbing groups of sapped robots, this gives him a good chunk of survivability.
Canteen
Über	Having a safety net in case of discovery can be useful.
Kritz	The Spy has poor damage output overall, and would probably be better off with a cheaper canteen.
Ammo	Sappers are essential to slow down fast robots, and having a freebie at your disposal can be a game-changer.
Return	If a fast robot gets through with the bomb, a Spy can teleport to the base and sap-n-stab them. It can also be used as an unconventional way to escape bad situations if one's Dead Ringer is not charged or not equipped, though this means the Spy has to take time returning to the enemy's backfield.