At the beginning of your end step, Toxrill's first ability triggers, putting a slime counter on each creature your opponents control.
Because your opponents' creatures are now 0/0 due to Godhead of Awe and Toxrill's static effects, the creatures die as a state-based action due to having zero toughness.
Repeat during each of your end steps.
Results
Reduce each opposing creature's toughness to zero during each of your end steps.