Mikaeus, the Unhallowed + Yahenni, Undying Partisan + Persistent Constrictor

Mikaeus, the Unhallowed

Yahenni, Undying Partisan

Persistent Constrictor

How it works

1. Activate Yahenni by sacrificing Persistent Constrictor.
2. When Persistent Constrictor dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
3. Resolve the Yahenni ability.
4. Activate Yahenni by sacrificing Persistent Constrictor.
5. When Persistent Constrictor dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
6. Resolve the Yahenni ability.
7. Repeat.

This clever loop relies on the brilliant interplay between Mikaeus, the Unhallowed and Persistent Constrictor, using the fact that having both +1/+1 and -1/-1 counters simultaneously causes them to annihilate each other as a state-based action. Because Mikaeus grants undying while Persistent Constrictor natively possesses persist, the snake can alternate between returning with a +1/+1 counter and a -1/+1 counter every time you sacrifice it to Yahenni, Undying Partisan. As Yahenni grows larger with each iteration, you generate an endless stream of sacrifice, death, and enter-the-battlefield triggers to overwhelm your opponents.