Den Protector
Creature — Human Warrior
Creatures with power less than this creature's power can't block it.
Megamorph (You may cast this card face down as a 2/2 creature for 
. 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, return target card from your graveyard to your hand.
Viktor Titov
Rulings
You compare Den Protector's power to the power of any creature trying to block it only as blockers are assigned. Once Den Protector has been legally blocked by a creature, changing the power of either creature won't change or undo the block.
(wotc • 2015-02-25)
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.
(wotc • 2015-02-25)
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.
(wotc • 2015-02-25)
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.
(wotc • 2015-02-25)
Printings
Rulings
You compare Den Protector's power to the power of any creature trying to block it only as blockers are assigned. Once Den Protector has been legally blocked by a creature, changing the power of either creature won't change or undo the block.
(wotc • 2015-02-25)
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.
(wotc • 2015-02-25)
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.
(wotc • 2015-02-25)
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.
(wotc • 2015-02-25)