Torch the Witness is a uncommon Sorcery card from Murders at Karlov Manor (MKM), collector number 146. Current market price: $0.18 (foil $0.19), TCGplayer market prices via Scryfall.
Torch the Witness deals twice X damage to target creature. If excess damage was dealt to that creature this way, investigate. (Create a Clue token. It's an artifact with "{2}, Sacrifice this token: Draw a card.")