Unshakable Tail
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.
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Official rulings (6) · Scryfall
You 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.
If 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.
Some 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.
Some 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.
If 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.
Clue 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.