One day in the depths of hell, Satan grew restless, so 12 terrible people were thrown into an arena and forced to kill one another. When they killed, they assumed the form of their victims. This war raged on for eternity, with nothing but pure chaos to feed the tired minds of the damned. This is Mors Arcium.
It is the very definition of chaos. Not only is there the heat of battle, but also floods, changes to physics itself, and visits from Satan himself. There's also a "random" difficulty, which will corrupt the gameplay in some pretty entertaining ways.