Reaper King + Overseer of the Damned + Xenograft

Reaper King

Overseer of the Damned

Xenograft

How it works

1. Cause a creature to enter the battlefield.
2. Reaper King triggers, destroying target nontoken creature an opponent controls.
3. The creature dies, triggering Overseer of the Damned, creating a 2/2 Zombie creature token.
4. The Zombie enters the battlefield as a Scarecrow due to Xenograft, triggering Reaper King, destroying target nontoken creature an opponent controls.
5. Repeat from step 3.
6. This loop will also repeat whenever another creature enters the battlefield under your control.