Mikaeus, the Unhallowed + Heartmender + Carrion Feeder

Mikaeus, the Unhallowed

Heartmender

Carrion Feeder

How it works

1. Activate Carrion Feeder 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. Resolve the Carrion Feeder ability.
4. Activate Carrion Feeder by sacrificing Heartmender.
5. When Heartmender dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
6. Resolve the Carrion Feeder ability.
7. Repeat.

This elegant loop relies on Mikaeus, the Unhallowed to grant undying to your non-Human creatures, cleverly supplementing the native persist ability printed on Heartmender. When you sacrifice Heartmender to Carrion Feeder, its persist ability returns it with a -1/-1 counter, but sacrificing it *again* triggers undying instead, returning it with a +1/+1 counter that immediately cancels out the existing -1/-1 counter as state-based actions occur. Because Heartmender's upkeep trigger helps reset its counters too, you can continuously feed it to Carrion Feeder to generate infinite sacrifice triggers, death triggers, and a massively pumped Carrion Feeder.