Yarus, Roar of the Old Gods + Karlov Watchdog + Bartolomé del Presidio + Iroh, Tea Master

Yarus, Roar of the Old Gods

Karlov Watchdog

Bartolomé del Presidio

Iroh, Tea Master

How it works

1. Donate Karlov Watchdog to an opponent.
2. During the opponent's turn, activate Bartolomé del Presidio by sacrificing a face-down creature you control.
3. When the creature dies, Yarus's second ability triggers, returning it from your graveyard to the battlefield face-down as a 2/2 creature, and then not turning it face-up due to Karlov Watchdog.
4. Resolve the Bartolomé del Presidio ability.
5. Repeat from step 2.

This ingenious loop relies on a clever lockdown provided by Karlov Watchdog, which you donate to an opponent using Iroh, Tea Master's combat trigger so they can't turn permanents face up during your turn. With that restriction in place, sacrificing a face-down creature to Bartolomé del Presidio sends it to the graveyard, where Yarus, Roar of the Old Gods immediately catches the death trigger and drags it right back to the battlefield face down. Because Karlov Watchdog forbids turning things face up on your turn, the creature stays trapped in that face-down state, letting you loop the sacrifice indefinitely to stack infinite +1/+1 counters on Bartolomé del Presidio while generating endless enter-the-battlefield, leave-the-battlefield, and death triggers.