721.2e If a merged permanent contains face-up and face-down components, the permanent’s status is determined by its topmost component. If a face-down permanent becomes a face-up permanent as a result of an object merging with it, other effects don’t count it as being turned face up.
721.2f If a merged permanent is turned face down, each face-up component that represents it is turned face down. If a face-down merged permanent is turned face up, each face-down component that represents it is turned face up.
721.2g A face-down merged permanent that contains an instant or sorcery card can’t be turned face up. If such a permanent would turn face up, its controller reveals it and leaves it face down. Abilities that trigger when a permanent is turned face up won’t trigger.
702.36e Any time you have priority, you may turn a face-down permanent you control with a morph ability face up. This is a special action; it doesn’t use the stack (see rule 116). To do this, show all players what the permanent’s morph cost would be if it were face up, pay that cost, then turn the permanent face up. (If the permanent wouldn’t have a morph cost if it were face up, it can’t be turned face up this way.) The morph effect on it ends, and it regains its normal characteristics. Any abilities relating to the permanent entering the battlefield don’t trigger when it’s turned face up and don’t have any effect, because the permanent has already entered the battlefield.
Quote from NightWatch »And am I correct in thinking that in the case of Gift of Doom, if it is on top of a mutated creature, any mutated creature beneath it has its abilities nullified when the card is turned face up, since the permanent is no longer a creature?
Quote from genini2 »
It still has those abilities, but they may no longer have any effect. For example flying on a non-creature permanent doesn't do anything, but it still has that ability. But if you were to somehow get Scavenging Ooze under Gift of Doom and then morph it the result would still have the ability to exile a card from a GY for G and even get counters even though it doesn't have p/t to modify.