Hidden Dragonslayer is a rare Creature — Human Warrior card from Murders at Karlov Manor Commander (MKC), collector number 69. Current market price: $0.21, 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.