Case of the Pilfered Proof

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.

Each Case has two special keyword abilities: to solve and solved.

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.

"Solved — [Triggered ability]" means "[Triggered ability]. This ability triggers only if this Case is solved." Triggered abilities use the word "when," "whenever," or "at." They're often written as "[Trigger condition], [effect]."

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.

The meaning of "solved" differs based on what type of ability follows it. "Solved — [activated ability]" means "[Activated ability]. Activate only if this Case is solved." Activated abilities contain a colon. They're generally written "[Cost]: [Effect]."

"To solve" abilities will check for their condition twice: once when the ability would trigger, and once when it resolves. If the condition isn't true at the beginning of your end step, the ability won't trigger at all. If the condition isn't true when the ability resolves, the Case won't become solved.

"To Solve — [condition]" means "At the beginning of your end step, if [condition] and this Case is not solved, it becomes solved."

Being solved is not part of a permanent's copiable values. A permanent that becomes a copy of a solved Case is not solved. A solved Case that somehow becomes a copy of a different Case stays solved.

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.

Once a Case becomes solved, it stays solved until it leaves the battlefield.

"Solved — [static ability]" means "As long as this Case is solved, [static ability]." Static abilities are written as statements, such as "Creatures you control get +1/+1" or "Instant and sorcery spells you cast cost {1} less to cast."

Cases don't lose their other abilities when they become solved.

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.