All creatures your opponents control will have base toughness 0, and die as a state-based action due to having 0 toughness unless there is another effect increasing its toughness.
Whenever a creature enters the battlefield under an opponent's control, it will have base toughness 0, and die as a state-based action due to having 0 toughness unless there is another effect increasing its toughness.
Results
Creatures opponents control die upon entering.
Reduce the toughness of creatures opponents control to 0.