Yahenni, Undying Partisan
Legendary Creature — Aetherborn Vampire
Haste
Whenever a creature an opponent controls dies, put a +1/+1 counter on Yahenni.
Sacrifice another creature: Yahenni gains indestructible until end of turn.
"The time for subtlety is over, darling."
2/2
Illustrated by
Tarkir: Dragonstorm Commander#202RareEnglishLegality
Rulings
Feb 9, 2017
If Yahenni and a creature an opponent controls die simultaneously (perhaps because they fought or were in combat together), Yahenni won't be on the battlefield as its triggered ability resolves. It can't be saved by the +1/+1 counter that would have been put on it.