Mikaeus, the Unhallowed + Goblin Bombardment + Grazing Kelpie

Mikaeus, the Unhallowed

Goblin Bombardment

Grazing Kelpie

How it works

1. Activate Goblin Bombardment by sacrificing Grazing Kelpie.
2. When Grazing 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 Grazing Kelpie.
5. When Grazing 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.