31 cards where the text includes “undying”

Butcher Ghoul (Duel Decks: Blessed vs. Cursed #53)
Demonlord of Ashmouth (Avacyn Restored #96)
Endling (Modern Horizons #89)
Evernight Shade (Commander 2014 #144)
Flayer of the Hatebound (Commander 2019 #144)
Garbage Elemental (Unstable #82b)
Geralf's Messenger (Dark Ascension #63)
Geralf's Mindcrusher (Dark Ascension #37)
Hancock, Ghoulish Mayor (Fallout #45)
Haunted One (Commander Legends: Battle for Baldur's Gate #654)
Hound of Griselbrand (Avacyn Restored #141)
Howlgeist (Avacyn Restored #182)
Mikaeus, the Unhallowed (Commander Masters #173)
Nardole, Resourceful Cyborg (Doctor Who #50)
Nearheath Stalker (Dark Ascension #100)
Phyrexian Midway Bamboozle (Unfinity Sticker Sheets #18)
Pyreheart Wolf (Dark Ascension #101)
Relentless Skaabs (Duel Decks: Blessed vs. Cursed #46)
Sightless Ghoul (Dark Ascension #73)
Stormbound Geist (Dark Ascension #51)
Strangleroot Geist (Dark Ascension #127)
Treacherous Pit-Dweller (Avacyn Restored #121)
Undying Beast (Portal #113)
Undying Evil (Dark Ascension #77)
Undying Flames (Saviors of Kamigawa #119)
Undying Rage (Dominaria Remastered #146)
Vengeful Vampire (Dark Ascension #78)
Vorapede (Commander 2020 #195)
Witch-king, Sky Scourge (Tales of Middle-earth Commander #511)
Yahenni, Undying Partisan (The Lost Caverns of Ixalan Commander #214)
Young Wolf (Dark Ascension #134)

The message was clear to Sorin—time to search for something else.