Blightbeetle + Mikaeus, the Unhallowed + Goblin Sharpshooter + Coveted Falcon

Blightbeetle

Mikaeus, the Unhallowed

Goblin Sharpshooter

Coveted Falcon

How it works

1. Activate Coveted Falcon by paying 1, turning it face up.
2. Coveted Falcon triggers, causing an opponent to gain control of Blightbeetle and causing you to draw a card.
3. Give Goblin Sharpshooter deathtouch, if needed.
4. Activate Goblin Sharpshooter by tapping it, dealing 1 damage to the additional creature and destroying it due to Goblin Sharpshooter's deathtouch.
5. When the creature dies, its undying ability and Goblin Sharpshooter trigger.
6. Resolve the creature's undying trigger, returning it from your graveyard to the battlefield without a +1/+1 counter on it due to Blightbeetle.
7. Resolve the Goblin Sharpshooter trigger, untapping it.
8. Repeat from step 4.

This clever engine hinges on giving Goblin Sharpshooter deathtouch so its ping can reliably destroy creatures and trigger itself to untap endlessly. The magic of the loop is sustained by Mikaeus, the Unhallowed, whose static ability grants undying to your non-Human creatures while simultaneously canceling out the required +1/+1 counter using Blightbeetle's passive prevention. Finally, Coveted Falcon acts as the clever vehicle to gift Blightbeetle over to your opponent, ensuring that your own creatures never accumulate the counters that would otherwise shut down the entire infinite loop.