Mikaeus, the Unhallowed + Goblin Bombardment + River Kelpie

Mikaeus, the Unhallowed

Goblin Bombardment

River Kelpie

How it works

1. Activate Goblin Bombardment by sacrificing River Kelpie.
2. When River Kelpie dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
3. When River Kelpie enters, its first ability triggers, causing you to draw a card.
4. Resolve the Goblin Bombardment ability.
5. Activate Goblin Bombardment by sacrificing River Kelpie.
6. When River Kelpie dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
7. When River Kelpie enters, its first ability triggers, causing you to draw a card.
8. Resolve the Goblin Bombardment ability.
9. Repeat.

This clever loop relies on the constant interplay between River Kelpie's native persist and the undying granted to it by Mikaeus, the Unhallowed. Because +1/+1 and -1/+1 counters annihilate each other as a state-based action, sacrificing River Kelpie to Goblin Bombardment allows it to alternate between returning with a -1/-1 counter and a +1/+1 counter indefinitely. Every time River Kelpie enters the battlefield from the graveyard, its own ability triggers to draw you a card while Goblin Bombardment provides a steady stream of damage to any target.