A sequel to the cooperative online shooter - Killing Floor - which came out in 2009 as a commercial version of a standalone Unreal Tournament 2004 modification. The sequel was prepared by the creators of the original – Tripwire Interactive, also known for another popular game modification, Red Orchestra. Just as its predecessor, the game features a negligible story, instead focusing on combat between a team of elite soldiers and hordes of mutants created in a series of experiments carried out by a medical corporation. Gameplay focuses on fighting off waves of enemies that precede a boss fight on the end of a round. After each round the team of players can regroup, repair damaged barricades, and spend money earned in combat on new weapons and ammo. Advancing to higher levels unlocks useful character abilities. This new game exceeds the last one in terms of graphics and features a realistic physics engine.