Blightbeetle + Ashnod's Altar + Wrong Turn

Blightbeetle

Ashnod's Altar

Wrong Turn

How it works

1. Donate Blightbeetle to an opponent
2. Activate Ashnod's Altar 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. Repeat from step 2.

This clever loop turns an ordinary undying creature into an endless engine by using Blightbeetle's passive static ability to shut down the self-limiting drawback of undying entirely. Since your opponent now controls the beetle thanks to Wrong Turn, their creatures—or in this case, your recurring sacrifice target—can never receive those pesky +1/+1 counters that normally stop undying from triggering a second time. You simply sacrifice the creature to Ashnod's Altar for a steady stream of colorless mana, watch it instantly return to the battlefield without a counter, and repeat the loop as many times as you desire.