Well this is downright horrifying.
A few players have found a curious glitch where Jason Vorhees refuses to stay down, even after experiencing brutalities that dismember him or behead him. Shoryuken explains that this happens because Jason has an "Unstoppable" stance, which allows him to revive himself -- even when he's technically not supposed to be able to do that.
Watch as Jason gets up after having half his body torn off in this video by Xhogar Varthus:
Here, Jason stands back up in Icey White Ryan's game after getting his head chopped off:
Damn. Well, we don't know him as an unstoppable horrific menace for nothing!