Blightbeetle + Ashnod's Altar + Blim, Comedic Genius

Blightbeetle

Ashnod's Altar

Blim, Comedic Genius

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 Blightbeetle's passive hate into a combo engine by pairing its ability to prevent +1/+1 counters on opponents' creatures with an undying creature you've generously donated away—perhaps using Blim, Comedic Genius to hand it over in the first place. Normally, an undying creature returns with a counter that shuts down further recursion, but since the opponent now controls the creature and Blightbeetle forbids those counters from being placed, the creature returns completely clean every single time. You then sacrifice it to Ashnod's Altar to generate infinite colorless mana while triggering an endless stream of enters-the-battlefield, leaves-the-battlefield, and death events.