Mikaeus, the Unhallowed + Grim Poppet + Thermopod

Mikaeus, the Unhallowed

Grim Poppet

Thermopod

How it works

1. Activate Thermopod by sacrificing Grim Poppet.
2. When Grim Poppet dies, its undying ability triggers, returning it from your graveyard to the battlefield without a +1/+1 counter on it due to its replacement effect.
3. Repeat.

This loop relies on Mikaeus, the Unhallowed to grant undying to Grim Poppet, ensuring that every time the Poppet hits the graveyard, it comes right back to the battlefield. Thermopod provides the necessary sacrifice outlet to trigger that undying return while simultaneously generating an endless stream of red mana. Because Grim Poppet enters the battlefield fresh each time, it gets to wipe away its own -1/-1 counters and start anew, turning an engine of endless sacrifices into an infinite source of red mana, creature triggers, and -1/-1 counter placement.