Mikaeus, the Unhallowed + Canker Abomination + Umbral Collar Zealot

Mikaeus, the Unhallowed

Canker Abomination

Umbral Collar Zealot

How it works

1. Activate Umbral Collar Zealot 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 Umbral Collar Zealot ability, and repeat from step 1.

This loop relies on Mikaeus, the Unhallowed to grant undying to your other non-Human creatures, turning Canker Abomination into an immortal sacrifice outlet for Umbral Collar Zealot. As long as the chosen opponent controls at least seven creatures, Canker Abomination enters the battlefield with enough -1/-1 counters to instantly nullify the +1/+1 counter from undying, causing it to die as a state-based action and immediately retrigger the cycle. By repeating this process, Umbral Collar Zealot lets you endlessly surveil your library while generating an infinite storm of sacrifices, leaves-the-battlefield triggers, and death triggers.