Surgeon Simulator 2013
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Surgeon Simulator 2013 is a game about performing surgery. It is infamous for its extremely convoluted control system, having the player control the hand directly instead of using premade motions.
The game has a TF2 related mission, a reenactment of Meet the Medic. Completing the mission awards the player with a Medic figurine that has a cryptic note attached to the bottom. Both Valve and Bossa studios have stated that it is not a part of any Valve related ARG. It was later revealed that the note was a part of an ARG to unlock the space missions in the game.