Hidden Dragonslayer is a rare Creature — Human Warrior card from Dragons of Tarkir (DTK), collector number 23. Current market price: $0.20 (foil $0.56), TCGplayer market prices via Scryfall.
Lifelink Megamorph {2}{W} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its megamorph cost and put a +1/+1 counter on it.) When this creature is turned face up, destroy target creature with power 4 or greater an opponent controls.