Killing Floor 2 is a cooperative first-person survival horror game developed by Tripwire Interactive. The game is based on events of the first Killing Floor. A biotech corporation Horzine attempts to create military clones, yet something goes wrong and now the mutant clones are spread all around Europe. Governments collapse and the infrastructure is almost non-existent. Up to 6 players spawn on the map in order to kill the boss. The players have to hold out 4, 7 or 10 waves of enemies after which the boss spawns. Each wave has more enemies and special mutants. After the end of a wave, the players can visit the trader, where they can buy weaponry and equipment. Players earn money and experience points for killing enemies. The more players there are on the map – the more enemies spawn. The difficulty level is also affected by the number of players. The only difference between singleplayer and multiplayer is in the number of players. The game features a class system. Players spawn with level 0 and can level themselves up to level 25. Each class is better in one field of combat. For example, medics have a speed boost and can heal other players while supports are able to seal the doors.