Mairsil, the Pretender + Blood Vassal + Endling + Cinderhaze Wretch

Mairsil, the Pretender

Blood Vassal

Endling

Cinderhaze Wretch

How it works

1. Activate Mairsil using Endling's third ability by paying , giving Mairsil undying until end of turn.
2. Activate Mairsil using Blood Vassal's ability by sacrificing it, adding .
3. Mairsil dies, triggering its undying ability, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
4. Activate Mairsil using Cinderhaze Wretch's second ability by putting a -1/-1 counter on it, untapping it.
5. Repeat.

This loop relies on Mairsil, the Pretender acting as a living archive of exiled powers, cage-knitting together the right activated abilities to create an engine of perpetual motion. By caging Endling, Mairsil gains its undying ability, ensuring that its eventual demise actually resurrects it with a +1/+1 counter. Meanwhile, having previously caged Blood Vassal allows Mairsil to sacrifice itself directly for black mana, which conveniently pays for the very rebirth it needs. Finally, Cinderhaze Wretch provides the crucial counter-balancing act: its ability lets Mairsil place a -1/+1 or -1/-1 counter on itself to untap, neutralizing the +1/+1 counter from undying and keeping the loop infinitely repeatable for boundless black mana.