Mairsil, the Pretender + Carnifex Demon + Cauldron of Souls + Blood Pet + Fervor

Mairsil, the Pretender

Carnifex Demon

Cauldron of Souls

Blood Pet

Fervor

How it works

1. Activate Mairsil using Cauldron of Souls' ability by tapping it, giving itself persist until end of turn.
2. Activate Mairsil using Blood Pet's ability by sacrificing it, adding .
3. When Mairsil dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
4. Activate Mairsil using Carnifex Demon's ability by paying and removing a -1/-1 counter from it, putting a -1/-1 counter on each other creature.
5. Repeat.

By feeding a suite of cored abilities directly into Mairsil, the Pretender, this loop turns your commander into a self-sustaining engine. You begin by exiling Cauldron of Souls and Blood Pet to cage counters, granting Mairsil the power to grant itself persist and sacrifice itself for black mana. Thanks to Fervor granting haste, Mairsil can act immediately without waiting around for summoning sickness. When the commander finally succumbs to sacrifice, persist brings it right back, where Carnifex Demon's caged ability steps in to strip away the lingering -1/-1 counter so the loop can start all over again.