Yuan-Ti Malison is a rare Creature — Snake Rogue card from Adventures in the Forgotten Realms (AFR), collector number 371. Current market price: $0.33 (foil $0.44), 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.)