You control a face-down creature whose front face is a permanent card.
Mana Needed
({2} magic symbol) ({U} magic symbol) available.
Steps
Donate
Karlov Watchdog to an opponent.
During the opponent's turn, activate
Phantom Train by sacrificing a face-down creature you control.
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.
Resolve the
Phantom Train ability.
Repeat from step 2.
Results
Infinite LTB.
Infinite ETB.
Infinite sacrifice triggers.
Infinite death triggers.
Infinite +1/+1 counters on a creature.
Metadata
In 0 decks according to EDHREC.
Bracket Tag
This combo has been estimated to be Exhibition (Bracket 1+).