Maha, Its Feathers Night, and Crovax, Ascendant Hero

Prerequisites

• Maha, Its Feathers Night on the battlefield
• Crovax, Ascendant Hero on the battlefield

Steps

1. All nonwhite 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 nonwhite 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

• Lock
• Nonwhite creatures opponents control die upon entering
• Reduce the toughness of most creatures opponents control