Blightbeetle + Yahenni, Undying Partisan + Coveted Falcon

Blightbeetle

Yahenni, Undying Partisan

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. Activate Yahenni by sacrificing the undying creature.
4. 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.
5. Resolve the Yahenni ability.
6. Repeat from step 3.

This intricate loop hinges on Blightbeetle's passive ability, which prevents opponents' creatures from ever receiving +1/+1 counters—a crucial rider that cleanly bypasses the usual safety valve on undying creatures and allows them to return from the graveyard endlessly. With that permanent restriction in place, you can continually feed a sacrificial engine using Yahenni, Undying Partisan, whose own triggered ability happily grows larger while providing a handy backup plan of granting itself indestructible. Meanwhile, the presence of Coveted Falcon allows you to cleanly hand off ownership of your pieces to an opponent (or bring them back into the fold), weaving a clever mechanical dance that generates an unbounded stream of sacrifices, enters-the-battlefield effects, and leaves-the-battlefield triggers.