Mairsil, the Pretender + Blood Vassal + Endling + Workhorse

Mairsil, the Pretender

Blood Vassal

Endling

Workhorse

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 Workhorse's ability by removing a +1/+1 counter from it, adding C.
5. Repeat.

This ingenious loop turns Mairsil, the Pretender into a self-sustaining engine by absorbing the exiled abilities of three devoted minions. By utilizing the activated ability granted by Endling, Mairsil gives itself undying so it can safely perish and return to the battlefield whenever you sacrifice it to Blood Vassal's mana-generating ability. This cycle provides an influx of black mana while naturally fueling the undying return that places a +1/+1 counter back onto Mairsil. From there, the counter can be immediately spent using the activated ability borrowed from Workhorse to produce colorless mana, clearing the counter just in time to repeat the entire deadly process anew.