Bug: Scream Fortress 2014 - Carnival of Carnage: once the tickets are successfully taken to the top of the Strong Man game, Marasmus will send all players into a team decided bumperkart death match. But also on this map Marasmus will periodically cast one of three spells over all players, one of which is underwater mode. Well it's actually under Jarate, but it's technically still called underwater mode. The system for Marasmus' spells runs independently of the bumperkart system and they sometimes overlap. But the spells are not supposed to affect the bumperkarts. However, if Marasmus happens to be casting a random spell, and that random spell is underwater mode, and is cast at the exact moment everybody is sent to the bumperkart track, a glitch happens where the bumperkart track is underwater mode as well. This causes zero gravity which makes dying almost impossible, and if the bumperkart game happens to be Falling Platforms, then the match will carry on indefinitely until a full team either leaves the server or swims down to the teeth for suicide. It also makes Duck Collection and Bumpercar Soccer extremely difficult to play. In bumperkart games, any Marasmus spells that happen to be cast as the bumperkart match starts (Big Heads, Melee Only, or Underwater) will linger in bumperkart mode without a time limit. Big head does not really effect the bumperkart games, and melee only has no effect at all, but underwater is a total game breaking game changer.
Bug: For the longest time, since they came out with taunting in the game, there has been a glitch where you can move while taunting. A player runs at a ledge and taunts right before they reach the edge. From the player's perspective, the view would switch to third person as it usually does while taunting, but only for a split second before snapping back to first person as the player goes over the edge and they can move unrestricted. And any dialog the character would say while taunting would be cut off. But to any other players watching, it would appear the player's model would continue the taunting animation, but drop off the ledge and be sliding around while taunting. This lead to an exploit as well involving the High Five Taunt that could be held indefinitely, and would throw off the player model's hit box and making it difficult to hit, especially troublesome for snipers. (This glitch has been fixed now as of the update of May 19th, 2014, preparing for the new taunts to be added to prevent exploiting).
Bug: Sometimes when a player wearing an Unusual hat leaves the server, the effect of the Unusual will stay hovering in the air where they last were and will stay there until the server resets. It will only be visible to some players though. For example, a player has on an Unusual hat with the Orbiting Planets effect. They leave the server and another player goes to the spot where they last were and can see just random miniature planets circling around in a spot levitating above the ground at about eye level.
Revealing mistake: Scream Fortress 2014 - Carnival of Carnage: Sometimes if you get killed while using the shrinking spell, and you are standing on a sloped or uneven surface, your body will get party stuck through the ground as it instantly goes back to regular size in death. And this can even cause where all that is sticking up from the ground is your head, as it hangs there.
Other mistake: Scream Fortress 2014 - Carnival of Carnage: When Marasmus casts the Giant Heads spell, if a player, especially one playing a Heavy, is wearing the Monoculous hat. Which is a large eyeball and lid that replaces the character's head. When this spell is cast, you can see the eyeball mask enlarge, but just the lid part, the purple and white of the eye vanishes completely. This allows you to see the character's head inside it and makes it look more like a space helmet. And then the insides of the eye lid are transparent from the insides, like a one way mirror.
Bug: Mann Vs Machine/Mannhattan: This is a rare glitch, but sometimes a Samurai Demo will get stuck in the Robot spawn zone at the top where there is a ramp. His feet will be stuck in the down ramp and he will be completely unable to move or be moved. This presents a huge problem as while in the spawn zone, all robots are invulnerable and he will appear to be in a consent state of Ubercharge. The Samurai Demos are enemies that must be destroyed before progression, so one getting stuck means you must reset the wave or the match, as you will be forever stuck otherwise.
Bug: Mann Vs. Machine: Often times if a player is too close to the explosion that happens when the wave is failed (meaning the robots pushed through and dropped the bomb), a player will die and the explosion will cause their ragdoll to get stuck in the ground, usually with just the head or torso protruding up from the ground. This can occasionally happen from other deaths in the MvM matches.
Continuity mistake: Spy: Despite them appearing brown in the player model, a BLU Spy will have white cigarettes in his Disguise Kit.