Blightbeetle + Bloodflow Connoisseur + Stiltzkin, Moogle Merchant

Blightbeetle

Bloodflow Connoisseur

Stiltzkin, Moogle Merchant

How it works

1. Donate Blightbeetle to an opponent
2. Activate Bloodflow Connoisseur 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 Bloodflow Connoisseur ability.
5. Repeat from step 2.

This clever loop relies on a clever interaction with Blightbeetle's static ability, which prevents opponents' creatures from ever receiving +1/+1 counters—a restriction that completely breaks the safety valve on the undying mechanic (implied in the steps as the sacrificed creature). Because that counter can never land, the undying creature can return to the battlefield endlessly whenever it hits the graveyard. Stiltzkin, Moogle Merchant sets the stage by using its activated ability to hand control of the Blightbeetle over to your opponent, locking down their board while leaving your side free to operate. Finally, Bloodflow Connoisseur provides the sacrificial outlet that starts the engine, converting that infinite resurrection cycle into an arbitrarily large vampire and limitless triggers.