FOILCheapest priced copy (Dragons of Tarkir): $0.49 at Card Kingdom, near mint, their price list as of .
Hidden Dragonslayer 
Creature — Human Warrior · 2/1 · Rare · Dragons of Tarkir Promos · #23s
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.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
3 printings · $0.49 to $1.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Dragons of Tarkir | 23 | Rare | $0.49 | $0.49 |
| Murders at Karlov Manor Commander | 69 | Rare | $0.49 | — |
| Dragons of Tarkir Promos | 23s | Rare | — | $1.49 |
3 rulings from Wizards of the Coast
- 25 February 2015Turning a face-down creature with megamorph face up and putting a +1/+1 counter on it is a special action. It doesn't use the stack and can't be responded to.
- 25 February 2015Megamorph is a variant of the morph ability. You can find more information on morph on cards with morph from the Khans of Tarkir set.
- 25 February 2015If a face-down creature with megamorph is turned face up some other way (for example, if you manifest a card with megamorph and then pay its mana cost to turn it face up), you won't put a +1/+1 counter on it.