Mikaeus, the Unhallowed + Phyrexian Altar + Putrid Goblin

Mikaeus, the Unhallowed

Phyrexian Altar

Putrid Goblin

How it works

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

This loop relies on a brilliant counter-cancellation mechanic enabled by Mikaeus, the Unhallowed, whose static ability grants undying to your non-Human creatures. When you sacrifice Putrid Goblin to Phyrexian Altar for mana, its persist ability triggers to bring it back with a -1/-1 counter. The next time you sacrifice Putrid Goblin, the -1/-1 counter and the new +1/+1 counter from Mikaeus, the Unhallowed's undying grant annihilate each other as a state-based action, resetting the goblin's clean slate. This allows Putrid Goblin to alternate endlessly between persist and undying triggers, fueling Phyrexian Altar for infinite colored mana and death triggers.