Yuan-Ti Malison is a rare Creature — Snake Rogue card from Adventures in the Forgotten Realms (AFR), collector number 86. Current market price: $0.35 (foil $0.36), TCGplayer market prices via Scryfall.
This creature can't be blocked as long as it's attacking alone. Whenever this creature deals combat damage to a player, venture into the dungeon. (Enter the first room or advance to the next room.)