Merchant of Truth

A creature attacks alone if it’s the only creature declared as an attacker during the declare attackers step (including creatures controlled by your teammates, if applicable). For example, exalted won’t trigger if you attack with multiple creatures and all but one of them are removed from combat. Similarly, creatures that enter the battlefield attacking later in combat won’t affect exalted abilities that have already triggered or resolved.

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.

If Merchant of Truth dies at the same time as one or more other nontoken creatures you control, its second ability will trigger for each of those creatures.

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.

If you control multiple Merchants of Truth, Clues you control will have multiple instances of exalted.

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.

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.

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.