Blightbeetle + Woe Strider + Bazaar Trader

Blightbeetle

Woe Strider

Bazaar Trader

How it works

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

This ingenious loop relies on a clever piece of asymmetrical disruption: by using Bazaar Trader to hand control of your Blightbeetle over to an opponent, its static ability turns off their ability to receive +1/+1 counters. With that restriction locked in place, you can continually cycle an undying creature into Woe Strider's sacrifice maw; when the creature tries to return with a counter, Blightbeetle nullifies it entirely, leaving the creature clean and ready to die all over again.