Mikaeus, the Unhallowed + Bloodied Ghost + Goblin Bombardment

Mikaeus, the Unhallowed

Bloodied Ghost

Goblin Bombardment

How it works

1. Activate Goblin Bombardment by sacrifiicing Bloodied Ghost.
2. When Bloodied Ghost dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it. When it enters, Bloodied Ghost will put a -1/-1 counter on itself, removing the +1/+1 counter.
3. Resolve the Goblin Bombardment ability.
4. Repeat.