Doors of Durin is a rare Legendary Artifact card from Tales of Middle-earth Promos (PLTR), collector number 199s. Current market price: — (foil $3.89), TCGplayer market prices via Scryfall.
Whenever you attack, scry 2, then you may reveal the top card of your library. If a creature card is revealed this way, put it onto the battlefield tapped and attacking. Until your next turn, it gains trample if you control a Dwarf and hexproof if you control an Elf.