Blightbeetle + Umbral Collar Zealot + Stiltzkin, Moogle Merchant

Blightbeetle

Umbral Collar Zealot

Stiltzkin, Moogle Merchant

How it works

1. Donate Blightbeetle to an opponent
2. Activate Umbral Collar Zealot by sacrificing the undying creature.
3. When the undying creature dies, its undying ability triggers, returning itself from your graveyard to the battlefield without a +1/+1 counter on it due to Blightbeetle.
4. Resolve the Umbral Collar Zealot ability.
5. Repeat from step 2.

This clever loop turns Stiltzkin, Moogle Merchant into a hostile delivery service by using its tap ability to gift Blightbeetle directly to an opponent. Once that Blightbeetle is firmly on the other side of the battlefield, its passive static ability completely forbids opponents' creatures from ever receiving +1/+1 counters. That blanket prohibition is the linchpin that breaks any undying creature paired with Umbral Collar Zealot: when you sacrifice that creature to fuel Umbral Collar Zealot's sacrifice cost and surveil 1, its undying trigger attempts to return it with a counter—which Blightbeetle immediately blocks, leaving the creature completely clean and ready to be sacrificed all over again for an infinite cycle of triggers.