In the Chaos Wastes, ‘Slaughter Bay’ level, ‘Defeat the Horde’ part (the finale part after ringing the bell), there is a spot where if you stand on it, the enemies will not be able to reach you because they will instantly die when they get near it. This spot is one of the two possible exits to this level.
Screenshots:
The part where enemies will instantly die is at this area encircled in red. I and Saltz are standing on the cheese spot.
Some players encourage the team to stand there, to avoid fighting enemies altogether:
Even monsters are affected.
A chaos spawn, just before reaching the spot:
And after reaching the spot:
