Creatures with power less than Den Protector's power can't block it. Megamorph {1}{G} When Den Protector is turned face up, return target card from your graveyard to your hand.
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.
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.
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.
2015-02-25
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.