Unshakable Tail is a rare Creature — Zombie Detective card from Murders at Karlov Manor Commander (MKC), collector number 339. Current market price: $0.42, TCGplayer market prices via Scryfall.
When this creature enters and at the beginning of your upkeep, surveil 1. Whenever one or more creature cards are put into your graveyard from your library, investigate. (Create a Clue token. It's an artifact with "{2}, Sacrifice this token: Draw a card.") {2}, Sacrifice a Clue: Return this card from your graveyard to your hand.