Horn of the Mark is a rare Legendary Artifact card from The Lord of the Rings: Tales of Middle-earth (LTR), collector number 241. Current market price: $0.40 (foil $1.00), TCGplayer market prices via Scryfall.
Whenever two or more creatures you control attack a player, look at the top five cards of your library. You may reveal a creature card from among them and put it into your hand. Put the rest on the bottom of your library in a random order.
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