Thorough Investigation is a rare Enchantment card from Forgotten Realms Commander (AFC), collector number 12. Current market price: $2.27, TCGplayer market prices via Scryfall.
Whenever you attack, investigate. (Create a Clue token. It's an artifact with "{2}, Sacrifice this token: Draw a card.") Whenever you sacrifice a Clue, venture into the dungeon. (Enter the first room or advance to the next room.)