Mikaeus, the Unhallowed + Bloodied Ghost + Umbral Collar Zealot

Mikaeus, the Unhallowed

Bloodied Ghost

Umbral Collar Zealot

How it works

1. Activate Umbral Collar Zealot by sacrifiicing Bloodied Ghost.
2. When Bloodied Ghost dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it. When it enters, Bloodied Ghost will put a -1/-1 counter on itself, removing the +1/+1 counter.
3. Resolve the Umbral Collar Zealot ability.
4. Repeat.

This clever loop turns Mikaeus, the Unhallowed into an engine for infinite value by granting undying to your other non-Human creatures. When you sacrifice Bloodied Ghost to Umbral Collar Zealot, Mikaeus's static ability brings the Ghost right back to the battlefield with a +1/+1 counter. However, Bloodied Ghost's own triggered ability causes it to enter with a -1/-1 counter, which instantly annihilates the +1/+1 counter through state-based actions. Because the Ghost ends up with zero counters, the undying safety net remains permanently primed, allowing you to feed Umbral Collar Zealot over and over again to surveil your entire library into your graveyard.