
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.)
Thorough Investigation has 2 printings, first in Forgotten Realms Commander (2021). EDHREC ranks it #7,263 among Commander cards. It appears most in Sefris of the Hidden Ways decks (4,422 on EDHREC). 1 public deck on TCG runs it. It has 11 official rulings.
Deck counts from EDHREC.
Cards that show up in the same decks on EDHREC.