Blightbeetle + Fateful Handoff + Carrion Feeder

Blightbeetle

Fateful Handoff

Carrion Feeder

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.

This clever loop uses Fateful Handoff to gift a crucial piece to your opponent, turning Blightbeetle's passive prevention of +1/+1 counters into a devastating restriction for them rather than you. With that block in place, Carrion Feeder's ability to repeatedly sacrifice your creatures and grow itself functions infinitely because the returning creatures can never receive the +1/+1 counters that would normally stop the loop from repeating.