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This article is about the boss. For the cosmetic item, see MONOCULUS!.
For the spell, see Magic spells.
Monoculus normal.png
Kill Icon
Killicon monoculus.png
Basic Information
Health: 8,000 (Level 1)

11,000 + 3,000n (Level n ≥ 2)

Damage Done: 150
Affected By:
• Battalion's Backup: Yes
• Bonk! Atomic Punch: Yes
• Candy Cane: No
• Chargin' Targe:
• Dead Ringer: Yes
• Gunboats: No
• Mini-crits: No
• ÜberCharge: Yes
Found On: Eyeaduct, Hellstone, Brimstone, Gravestone, Slasher, Bloodwater
...Everyone thinks I'm just a one-eyed bloody monster...
The Demoman lamenting his eye

MONOCULUS is the RED Demoman's missing eye, haunted, and grown to monstrous size by the Bombinomicon. It was summoned by Merasmus when the RED Soldier broke his staff. In the Bombinomicon comic, it is depicted as a large brown floating eye that fires purple rocket-like eyeballs.


MONOCULUS spawns out of Eyeaduct's control point every 3 minutes (with a random variation of 30 seconds) when at least 10 players are on the server and assigned to a team. Standing on the Control point while MONOCULUS spawns disintegrates the respective player. The players have 2 minutes to defeat it, or it disappears. While MONOCULUS is alive, the point resets to neutral ownership and is unable to be captured, rendering the round temporarily unwinnable for either team. MONOCULUS's remaining health is displayed as a bar in a box near the top center of the screen. It fires eye-shaped projectiles that are guaranteed critical hits. When enraged, it shoots three of these projectiles in quick succession. Its projectiles can be deflected, similar to the Soldier's rockets.

At random intervals, it teleports, leaving a swirling, purple vortex where it last was. The portals have attraction effects on nearby players to help players enter more effectively. Players are able to enter this vortex, and are taken to the Underworld. Upon entering the Underworld, the player spawns on an island and take continuous periodic damage. Another portal is across from the player on another island. Upon exiting the Underworld, a player is spawned at one end of the map, invulnerable, crit boosted, overhealed to 200% their maximum health, and having a speed buff as if hit by the Disciplinary Action. Damaging MONOCULUS while in this state stuns it and causes it to sink to the ground for a few seconds and start groaning.

Critical hits anger MONOCULUS in a way that accelerates its rate of fire. In this mode, the eyeball projectiles' speed matches the Rocket Launcher's projectiles' speeds and MONOCULUS flawlessly leads its targets until it calms itself. It is worth noting that MONOCULUS resists 50% of critical damage, resulting in critical hits dealing double damage as opposed to the usual triple damage. MONOCULUS also has a natural damage resistance against Miniguns and Flamethrowers. However, damage fall-off and ramp-up is completely ignored, meaning a successful hit always deals the base damage of the corresponding weapon. Thrown weapons, such as Mad Milk, bounce harmlessly off MONOCULUS. When MONOCULUS is angry, its iris changes from brown to a bright red colour as well as its skin which changes to a light brown.

Upon MONOCULUS's defeat, it first changes into a massive Jarate explosion, soaking any nearby players. An opened Bombinomicon then spawns, surrounded by a red swirling vortex. This Bombinomicon constantly points at the player who killed MONOCULUS, tilting and rotating to follow the player. Players who enter this are teleported to Loot Island in the Underworld, at the base of a hill. On top of this hill is a large skull and a cage which contains the Bombinomicon. The cage slowly descends into the ground where players can collect the Bombinomicon, awarding the "Dive into a Good Book" achievement. Some time after the book is available, a laugh is heard, then the hill is filled with exploding eyeball projectiles, killing any player still standing upon it, and the cage covers the Bombinomicon again.

Defeating MONOCULUS automatically grants the "Optical Defusion" achievement, which gives the player the MONOCULUS! cosmetic.

As of the November 2, 2011 Patch, MONOCULUS now has a level. Each time it is defeated, it levels up and receives higher health points. When MONOCULUS escapes, its level returns to 1. The maximum defined limit for MONOCULUS's level is 32,767.


Main article: Community Eyeaduct strategy
Main article: MONOCULUS match-ups

Related achievements

Monoculus angry.png Eye-chievements

Optical Defusion
Optical Defusion


Leaderboard class scout.png Scout

Foul Territory
Foul Territory
Cause an environmental death by stunning or slowing an enemy.
Fall Classic
Fall Classic
Cause an environmental death or suicide using the Force-A-Nature's knockback.

Leaderboard class soldier.png Soldier

Death From Below
Death From Below
Kill 10 opponents who are airborne with the Direct Hit.

Leaderboard class pyro.png Pyro

Dead Heat
Dead Heat
Kill an enemy in the same second that he kills you.

Leaderboard class demoman.png Demoman

He Who Celt It
He Who Celt It
Use the Sticky Launcher to kill an enemy player via environmental damage.

Leaderboard class heavy.png Heavy

Crock Block
Crock Block
Survive a direct hit from a critical rocket.

Update history

October 27, 2011 Patch (Very Scary Halloween Special)
  • Introduced MONOCULUS to the game.

October 28, 2011 Patch

  • Fixed a client crash that could occur while loading the map if MONOCULUS is killed or stunned.
  • [Undocumented] Fixed shooting MONOCULUS with bullet-firing weapons leaving the decals of impacted concrete.

November 2, 2011 Patch

  • MONOCULUS receives a faster firing rate and higher HP each time he respawns. This is indicated by levels.

September 4, 2012 Patch

  • Fixed Monoculus health bar not showing when Monoculus spawns.

November 2, 2012 Patch

  • Updated the health bar for Merasmus and Monoculus.

November 10, 2016 Patch

  • Updated the spawn/death sounds for Monoculus and Merasmus to remove the Horseless Headless Horsemann sound effects.

June 21, 2022 Patch

  • Fixed laggy animations on Halloween bosses, skeletons, ghosts and other ghoul-like beings.


  • If two players from different teams enter the Underworld portal at the same time, both may get stuck in mid air after teleporting. They get un-stuck if either player dies or commits suicide.
  • If MONOCULUS is not defeated and leaves, its health bar may persist on the HUD.
  • When MONOCULUS is active, the message telling players the point cannot be captured says "Waiting for teammate", which is incorrect.
  • Killing someone with a deflected eyeball projectile still counts as a MONOCULUS kill.
  • Being killed by standing on the control point when MONOCULUS emerges or from a pumpkin bomb detonated by its eyeball projectiles counts as a suicide/environmental death.
  • If a player hits one of the MONOCULUS projectiles with a Sandman's ball or Wrap Assassin's bauble, it freezes the projectile in place.
  • The game does not log that a building is destroyed by MONOCULUS.


  • Mono is Latin prefix meaning 'one,' and Oculus is a Latin root meaning 'eye,' so "MONOCULUS" literally translates to 'one eye.'
  • MONOCULUS recalls The Mighty Thor 292 (February 1980), If an Eye Offend Thee...! wherein Odin's Eye is introduced as a giant disembodied floating eyeball shooting forth jets of fire. See also: Odin reference in War!.
  • MONOCULUS' voice clips are slowed down or low-pitched versions of those of the Demoman.
  • In The Naked and the Dead (Page 91-92), the Medic describes multiple instances of Demoman's eye turning into a monster that differ from MONOCULUS' appearance in-game, specifically: growing bat wings, "dracula," "brain-in-a-jar," and "knife-wielding ventriloquist dummy" eyes.
    • The Medic also references a time where MONOCULUS went back in time and tried to become the Mercenaries' parents.
  • In Helltower, the "invokum monoculus" spell summons a ghostly team-colored MONOCULUS that begins to attack enemies. Should both teams summon a MONOCULUS, they may attack each other.
  • Upon typing ent_create eyeball_boss in console while sv_cheats is turned on, the BLU Helltower version appears and only attacks the RED team.
    • ent_create eyeball_boss teamnum 2 makes a RED MONOCULUS, and ent_create eyeball_boss teamnum 5 makes the original MONOCULUS.


See also