Blightbeetle + Carrion Feeder + Switcheroo

Blightbeetle

Carrion Feeder

Switcheroo

How it works

1. Donate Blightbeetle to an opponent
2. Activate Carrion Feeder 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 Carrion Feeder ability.
5. Repeat from step 2.

By using Switcheroo to hand your opponent a Blightbeetle, you weaponize its static ability—turning its restriction against +1/+1 counters into the engine that fuels an infinite sacrifice loop. Normally, recurring a creature with undying would be cut short by the counter it returns with, but Blightbeetle's passive text ensures those counters are cleanly prevented from ever landing. This allows Carrion Feeder to repeatedly devour the same undying threat without ever running out of room for fresh +1/+1 counters, generating an endless cascade of leaves-the-battlefield, enters-the-battlefield, and death triggers.