Mephidross Vampire + Walking Ballista

Mephidross Vampire
Walking Ballista

Requires
Mephidross Vampire must be on the battlefield. Walking Ballista must be on the battlefield. Walking Ballista has at least two +1/+1 counters on it.
Steps
  1. Activate Walking Ballista's second ability by removing a +1/+1 counter from it, dealing 1 damage to any creature an opponent controls.
  2. Walking Ballista 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.