Yurei, Shadowalker

Ward - Sacrifice a creature and mill a card
Commander Ninjutsu {u}{b}{r}
Whenever Yurei, Shadowalker deals damage to a player, you may reduce the cost of your partner commander by {2}. If your other commander is already on the battlefield you instead create a Legendary 5/5 Red Demon token with Menace and Infect.
Partner (The Heirs)