Ainok Survivalist

Megamorph {1}{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.)
When Ainok Survivalist is turned face up, destroy target artifact or enchantment an opponent controls.

Murders at Karlov Manor Commander

The List

Commander 2019

Masters 25

Dragons of Tarkir

If 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.

Megamorph is a variant of the morph ability. You can find more information on morph on cards with morph from the Khans of Tarkir set.

Turning 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.