Blightbeetle + Ashnod's Altar + Stiltzkin, Moogle Merchant

Blightbeetle

Ashnod's Altar

Stiltzkin, Moogle Merchant

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 loop transforms a sacrifice engine into an infinite mana generator by weaponizing a rule interaction around counters. By using Stiltzkin, Moogle Merchant to hand Blightbeetle over to your opponent, you establish a permanent static tax that prevents their creatures from receiving +1/+1 counters. When paired with an undying creature sacrificed to Ashnod's Altar, Blightbeetle's passive ability ensures the returning creature never picks up the counter that would normally shut down its ability to keep recurring, letting you repeatedly cash it in for colorless mana.