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.

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.

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.

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.

If a Clue you control is already a creature when Tangletrove Kelp’s second ability resolves, Tangletrove Kelp’s second ability will overwrite any previous effects that set that creature’s power and toughness to specific numbers. Effects that otherwise modify its power and toughness will still apply no matter when they took effect. The same is true for +1/+1 counters.

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.

Clues you control will keep any abilities they previously had while they’re creatures.