Mikaeus, the Unhallowed + Goblin Bombardment + Plague Belcher

Mikaeus, the Unhallowed

Goblin Bombardment

Plague Belcher

How it works

1. Activate Goblin Bombardment by sacrificing Plague Belcher.
2. When Plague Belcher dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
3. When Plague Belcher enters the battlefield, it triggers, putting a -1/-1 counter on it.
4. Resolve the Goblin Bombardment ability
5. Repeat.