Toxrill, the Corrosive | Maha, Its Feathers Night

Cards

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
Maha and
Toxrill's static effects, the creatures die as a state-based action due to having zero toughness unless there is an effect boosting their toughness.
Repeat during each of your end steps.

Reduce the toughness of opponents' creatures to 0 during each of your end steps.