Mairsil, the Pretender + Carnifex Demon + Cauldron of Souls + Blood Vassal + Urabrask the Hidden

Mairsil, the Pretender

Carnifex Demon

Cauldron of Souls

Blood Vassal

Urabrask the Hidden

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 Vassal'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.

This clever loop turns Mairsil, the Pretender into a self-sustaining engine by utilizing a cage counter to absorb the activated abilities of three different cards in exile. With Urabrask the Hidden on the board granting haste so Mairsil can immediately tap, you can invoke Cauldron of Souls to grant Mairsil persist, then sacrifice it to Blood Vassal's ability for a surge of black mana. When Mairsil dies, its newly acquired persist returns it to the battlefield, where Carnifex Demon's caged ability lets you pay black mana and remove the resulting -1/-1 counter to clear the way and reset the loop infinitely.