25 Feb 2015
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.
25 Feb 2015
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.
25 Feb 2015
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.
25 Feb 2015
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.