Mairsil, the Pretender + Endling + Cauldron of Souls + Blood Pet + Mass Hysteria

Mairsil, the Pretender

Endling

Cauldron of Souls

Blood Pet

Mass Hysteria

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 Endling's third ability by paying , giving Mairsil undying until end of turn.
5. Activate Mairsil using Blood Pet's ability by sacrificing it, adding .
6. When Mairsil dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
7. Repeat.

This loop turns Mairsil, the Pretender into an unstoppable engine by feeding on exiled power and the chaotic speed of Mass Hysteria, which ensures our commander can tap and activate abilities the very turn it arrives. By caging Cauldron of Souls and Endling, Mairsil learns how to grant itself both persist and undying; because +1/+1 counters and -1/+1 counters annihilate each other when placed on a creature, alternating between these two triggered abilities prevents counters from permanently sticking. Sacrificing Mairsil to Blood Pet's mana ability along the way fuels the black mana required for Endling's activation while generating an endless stream of sacrificial offerings.