Mairsil, the Pretender + Blood Vassal + Endling + Lunar Avenger

Mairsil, the Pretender

Blood Vassal

Endling

Lunar Avenger

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 Lunar Avenger's ability by removing a +1/+1 counter from it.
5. Repeat.