Yarus, Roar of the Old Gods + Karlov Watchdog + Phantom Train + Coveted Falcon

Yarus, Roar of the Old Gods

Karlov Watchdog

Phantom Train

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 Karlov Watchdog and causing you to draw a card.
3. During the opponent's turn, activate Phantom Train by sacrificing a face-down creature you control.
4. 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.
5. Resolve the Phantom Train ability.
6. Repeat from step 3.

This intricate loop turns the mechanics of morph and disguise inside out by weaponizing the rules of control and turn order. You begin by paying {1}{U} to cast Coveted Falcon using its disguise ability, then turn it face up so that its trigger hands Karlov Watchdog over to an opponent. That handoff is the linchpin of the whole operation: because Karlov Watchdog's static ability prevents permanents your opponents control from being turned face up *during your turn*, it now applies to that very watch dog itself on the opponent's turn, locking it and any other facedown permanents in a permanent face-down limbo. With that safety measure in place, you can activate Phantom Train on your opponent's turn by sacrificing a face-down creature. That death triggers Yarus, Roar of the Old Gods to pull the sacrificed creature straight back from the graveyard onto the battlefield face down as a 2/2, neatly bypassing Yarus's usual self-turn-up clause because Karlov Watchdog forbids it, readying the loop to repeat indefinitely for infinite sacrifices, triggers, and growth on Phantom Train.