Cheapest priced copy (Murders at Karlov Manor Commander): $0.49 at Card Kingdom, near mint, their price list as of .
Innocuous Researcher 
Creature — Centaur Detective · 3/4 · Rare · Murders at Karlov Manor Commander · #348
Parley — Whenever this creature attacks, each player reveals the top card of their library. For each nonland card revealed this way, you investigate. Then each player draws a card.
At the beginning of your end step, you may untap all lands you control. If you do, you can't cast spells until your next turn.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
2 printings · $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Murders at Karlov Manor Commander | 38 | Rare | $0.49 | — |
| Murders at Karlov Manor Commander | 348 | Rare | $0.49 | — |
7 rulings from Wizards of the Coast
- 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 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.
- 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 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 2024Except in some very unusual cases, the card each player reveals is the one they’ll draw.
- 2 February 2024There’s no window for you to cast spells after untapping all lands you control but before the “you can’t cast spells” portion of Innocuous Researcher’s last ability takes effect. Once that ability resolves, it doesn’t matter whether Innocuous Researcher stays on the battlefield; you’ll still be unable to cast spells until your next turn begins.
- 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.