Yahenni, Undying Partisan

Mana cost: {2}{B}
Type: Legendary Creature — Aetherborn Vampire
Power / toughness: 2 / 2
Set: Aether Revolt Promos #74p (rare)
Price: $3.88 USD

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.

Yahenni, Undying Partisan has 12 printings, first in Aether Revolt (2017). EDHREC ranks it #1,038 among Commander cards. It appears most in Edgar Markov decks (20,933 on EDHREC). 4 public decks on TCG run it. It has 1 official ruling.

Legality

commander: legal
legacy: legal
vintage: legal
pauper: not legal
modern: legal
pioneer: legal
standard: not legal
brawl: legal

Public decks that run Yahenni, Undying Partisan

20 Ways to Win, led by Go-Shintai of Life's Origin
Blood Rites - The Lost Caverns of Ixalan Commander, led by Clavileño, First of the Blessed
Mardu Surge - Tarkir: Dragonstorm Commander, led by Zurgo Stormrender
Witherbloom Pestilence - Secrets of Strixhaven, led by Dina, Essence Brewer

Commanders that run Yahenni, Undying Partisan most

Deck counts from EDHREC.

Edgar Markov: 20,933 decks
Teysa Karlov: 8,607 decks
Zurgo Stormrender: 8,091 decks
Clavileño, First of the Blessed: 8,052 decks
Marchesa, the Black Rose: 6,798 decks
Dina, Essence Brewer: 5,465 decks
Sephiroth, Fabled SOLDIER // Sephiroth, One-Winged Angel: 5,245 decks
Elenda, the Dusk Rose: 3,647 decks

Often played with Yahenni, Undying Partisan

Cards that show up in the same decks on EDHREC.

Rulings

2017-02-09: 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.