Mephidross Vampire + Triskelion

Mephidross Vampire
Triskelion

Requires
Mephidross Vampire must be on the battlefield. Triskelion must be on the battlefield. Triskelion has at least one +1/+1 counter on it.
Steps
  1. Activate Triskelion by removing a +1/+1 counter from it, dealing 1 damage to any creature an opponent controls.
  2. Triskelion triggers, putting a +1/+1 counter on itself.
  3. Repeat as desired.
  4. You may also repeat this loop whenever a creature enters the battlefield under an opponent's control.
Results
Destroy all creatures that enter the battlefield under an opponent's control. Destroy any number of creatures opponents control. Infinite damage to creatures.