Blightbeetle + Ashnod's Altar + Bazaar Trader

Blightbeetle

Ashnod's Altar

Bazaar Trader

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 relies on a specific interaction with Blightbeetle, whose static ability prevents your opponents' creatures from ever receiving +1/+1 counters. By using Bazaar Trader to hand control of that Blightbeetle over to your opponent, you completely turn off the built-in safety valve of any creature you own with the undying mechanic. With that counter-prevention firmly in place on your opponent's side of the board, you can repeatedly sacrifice that undying creature to Ashnod's Altar for colorless mana; because the creature returns without a counter, it dies endlessly to fuel a continuous loop of sacrifices, triggers, and infinite colorless mana.