Yarus, Roar of the Old Gods + Karlov Watchdog + Altar of Dementia + Bazaar Trader

Yarus, Roar of the Old Gods

Karlov Watchdog

Altar of Dementia

Bazaar Trader

How it works

1. Activate Bazaar Trader by tapping it, giving control of Karlov Watchdog to an opponent.
2. During the opponent's turn, activate Altar of Dementia 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 Altar of Dementia ability.
5. Repeat from step 2.