Mikaeus, the Unhallowed + Canker Abomination + Altar of Dementia

Mikaeus, the Unhallowed

Canker Abomination

Altar of Dementia

How it works

1. Activate Altar of Dementia by sacrificing Canker Abomination.
2. When Canker Abomination dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
3. When Canker Abomination enters the battlefield, it triggers, putting a number of -1/-1 counters on it equal to the number of creatures an opponent controls.
4. If the opponent had seven or more creatures, Canker Abomination will die as a state-based action due to having 0 or less toughness. If this occurs, repeat steps 2 through 4 infinitely.
5. Otherwise, resolve the Altar of Dementia ability, and repeat from step 1.