Mikaeus, the Unhallowed + Ashnod's Altar + River Kelpie

Mikaeus, the Unhallowed

Ashnod's Altar

River Kelpie

How it works

1. Activate Ashnod's Altar 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. Activate Ashnod's Altar by sacrificing River Kelpie.
5. When River Kelpie dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
6. When River Kelpie enters, its first ability triggers, causing you to draw a card.
7. Repeat.

This ingenious loop relies on the brilliant counterplay between two opposing mechanics granted to River Kelpie: its native persist and the undying ability bestowed upon it by Mikaeus, the Unhallowed. Because a +1/+1 counter and a -1/-1 counter will annihilate each other as a state-based action upon entering the battlefield, sacrificing the Kelpie to Ashnod's Altar allows it to alternate endlessly between returning via undying and returning via persist. Every single time the Kelpie re-enters the graveyard and returns, its own entry trigger lets you draw a card while Ashnod's Altar continuously fuels your mana pool with colorless energy.