Cheapest priced copy (Dragons of Tarkir): $0.35 at Card Kingdom, near mint, their price list as of .
Salt Road Ambushers 
Creature — Dog Warrior · 3/3 · Uncommon · Murders at Karlov Manor Commander · #184
Whenever another permanent you control is turned face up, if it's a creature, put two +1/+1 counters on it.
Megamorph {3}{G}{G} (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.)
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
2 printings · $0.35 to $0.79 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Dragons of Tarkir | 198 | Uncommon | $0.35 | $0.79 |
| Murders at Karlov Manor Commander | 184 | Uncommon | $0.35 | — |
4 rulings from Wizards of the Coast
- 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.
- 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 2015The face-down permanent must be a creature both before it's turned face up and when the triggered ability resolves to have +1/+1 counters placed on it.