Hauntwoods Shrieker is a mythic Creature — Beast Mutant card from Duskmourn: House of Horror (DSK), collector number 349. Current market price: $1.66 (foil $2.31), TCGplayer market prices via Scryfall.
Whenever this creature attacks, manifest dread. (Look at the top two cards of your library. Put one onto the battlefield face down as a 2/2 creature and the other into your graveyard. Turn it face up any time for its mana cost if it's a creature card.) {1}{G}: Reveal target face-down permanent. If it's a creature card, you may turn it face up.