Mikaeus, the Unhallowed + Phyrexian Altar + Heartmender

Mikaeus, the Unhallowed

Phyrexian Altar

Heartmender

How it works

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

This clever loop turns Mikaeus, the Unhallowed into an engine for infinite mana and triggers by granting undying to other non-Human creatures. When you feed Heartmender into the Phyrexian Altar, its native persist ability brings it back with a -1/-1 counter, but Mikaeus immediately overrides this limitation on the next sacrifice by granting undying instead, returning it with a +1/+1 counter. Because these two opposing counters instantly annihilate each other through state-based actions, Heartmender is completely reset to zero counters every cycle. This interplay lets you endlessly sacrifice and recur the same creature for infinite colored mana, death triggers, and sacrifice triggers.