Maha, Its Feathers Night, and Kaervek, the Spiteful

Prerequisites

• Maha, Its Feathers Night on the battlefield
• Kaervek, the Spiteful on the battlefield

Steps

1. 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
2. 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

• Reduce each opposing creature's toughness to zero
• Creatures opponents control die upon entering the battlefield