Cheapest priced copy (Murders at Karlov Manor Commander): $0.69 at Card Kingdom, near mint, their price list as of .
Unshakable Tail 
Creature — Zombie Detective · 3/2 · Rare · Murders at Karlov Manor Commander · #29
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.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
2 printings · $0.69 to $0.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Murders at Karlov Manor Commander | 29 | Rare | $0.69 | — |
| Murders at Karlov Manor Commander | 339 | Rare | $0.99 | — |
6 rulings from Wizards of the Coast
- 2 February 2024You can't sacrifice a Clue to pay multiple costs. For example, you can't sacrifice a Clue token to activate its own ability and also to activate Alquist Proft, Master Sleuth's ability.
- 2 February 2024If an effect puts multiple cards from a library into a graveyard, all of those cards move at the same time. For example, when Aftermath Analyst's enters the battlefield triggered ability resolves, you'll mill three cards at once. If one or more of those cards are creature cards, Unshakable Tail's second ability will trigger.
- 2 February 2024Some spells and abilities that investigate may require targets. If each target chosen is an illegal target as that spell or ability tries to resolve, it won't resolve. You won't create any Clue tokens.
- 2 February 2024Some abilities trigger "whenever you sacrifice a Clue". Those abilities trigger whenever you sacrifice a Clue for any reason, not just to activate a Clue's activated ability.
- 2 February 2024If an effect refers to a Clue, it means any Clue artifact, not just a Clue artifact token. For example, you can sacrifice Wrench to pay for Alquist Proft, Master Sleuth's activated ability.
- 2 February 2024Clue is an artifact type. Even though it appears on some cards with other permanent types, it's never a creature type, a land type, or anything but an artifact type.