Mikaeus, the Unhallowed + Goblin Bombardment + Trapjaw Kelpie

Mikaeus, the Unhallowed

Goblin Bombardment

Trapjaw Kelpie

How it works

1. Activate Goblin Bombardment by sacrificing Trapjaw Kelpie.
2. When Trapjaw Kelpie dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
3. Resolve the Goblin Bombardment ability.
4. Activate Goblin Bombardment by sacrificing Trapjaw Kelpie.
5. When Trapjaw Kelpie dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
6. Resolve the Goblin Bombardment ability.
7. Repeat.