Ravenloft Adventurer is a rare Creature — Human Rogue Assassin card from Battle for Baldur's Gate Promos (PCLB), collector number 142s. Current market price: — (foil $1.48), TCGplayer market prices via Scryfall.
When this creature enters, you take the initiative. If a creature an opponent controls would die, instead exile it and put a hit counter on it. Whenever this creature attacks, if you've completed a dungeon, defending player loses 1 life for each card they own in exile with a hit counter on it.