Shay Cormac + Agatha's Soul Cauldron + Walking Ballista

Shay Cormac

Agatha's Soul Cauldron

Walking Ballista

How it works

1. Give Shay Cormac deathtouch, if needed.
2. Activate Shay Cormac using Walking Ballista's second ability by removing a +1/+1 counter from it, targeting a creature an opponent controls.
3. Shay Cormac's first ability triggers, putting a bounty counter on the targeted creature.
4. Resolve the Shay Cormac ability from step 2, dealing 1 damage to the creature and killing it due to Shay Cormac's deathtouch.
5. When the creature dies, Shay Cormac's second ability triggers, putting two +1/+1 counters on it.
6. Repeat from step 2.
7. If the method giving Shay Cormac deathtouch lasts indefinitely, you may repeat this loop whenever a creature enters the battlefield under an opponent's control.