Heartmender + Thran Vigil + Yahenni, Undying Partisan

Heartmender

Thran Vigil

Yahenni, Undying Partisan

How it works

1. Activate Yahenni by sacrificing Heartmender.
2. When Heartmender dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
3. Thran Vigil triggers, putting a +1/+1 counter on Heartmender.
4. Resolve the Yahenni ability.
5. Repeat.

This loop transforms Yahenni, Undying Partisan into an absolute engine by feeding it your own creatures as sacrifices. Whenever Heartmender goes to the graveyard, its persist ability brings it right back, but with a lingering -1/-1 counter that would normally spell doom for its resilience. Thankfully, Thran Vigil triggers the exact moment Heartmender leaves your graveyard, slipping a +1/+1 counter onto it which immediately neutralizes that -1/-1 counter via state-based actions. With its slate wiped clean, Heartmender is ready to be sacrificed all over again to repeat this infinite cycle of death and rebirth.