Blightbeetle + Fateful Handoff + Yahenni, Undying Partisan

Blightbeetle

Fateful Handoff

Yahenni, Undying Partisan

How it works

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

This devious loop transforms a humble bug into an absolute engine by leveraging Blightbeetle's passive static ability, which prevents opponents' creatures from ever receiving +1/+1 counters. Because of this restriction, any creature you donate to an opponent via Fateful Handoff that possesses an undying-style return trigger will miraculously slip past its mechanical penalty; when it dies, it returns completely fresh. You then use Yahenni, Undying Partisan as the sacrifice outlet to continually reap those death triggers, fueling a perpetual cycle of sacrifice and rebirth.