This came up in a conversation among a group of friends who enjoy creating and then solving judge-busters. Warning: Corner case scenario ahead!

What happens if you have a morph creature in play (not a creature with morph, but a face-down creature) with a Deceiver of Form, and the morph creature becomes a copy of something?

1) What are the characteristics of the morph? (including non-copiable status such as face up/face down)

2) Assuming the morph creature has the Morph ability, does it retain the Morph ability? Does your answer change if it is a Manifest or an illusion (from Illusionary Mask instead?

3) If it is turned face up for any reason, such as Break Open (whether the answer to (2) is true or false), what are its characteristics?

4) If the card that was revealed to Deceiver has the morph ability, does the face-down creature gain the morph ability of the revealed card?

Thanks.

Edited Lyle Waldman (Feb. 2, 2016 12:11:18 AM)

The rule you and your friends are looking for is 707.10, which directly addresses the interaction of copy effects with being face-down.

707.10. If a face-down permanent becomes a copy of another permanent, its copiable values become the copiable values of that permanent, as modified by its face-down status. Its characteristics therefore remain the same: the characteristics listed by the ability or rules that allowed it to be turned face down. However, if it is turned face up, its copiable values become the values it copied from the other permanent. See rule 706.3.

This means:

1) The face-down creature is a 2/2 with no name, creature types, or other characteristics, just as it was before.

2) If the face-down creature has become a copy of something without morph (or megamorph), you are unable to turn it face-up using morph, because in order to do that, you need to check what the permanent's morph cost would be if it were face-up, as laid out in 702.36e. And since it's been turned into a copy of something that doesn't have morph, it wouldn't have a morph cost if it's face-up.

Manifest, on the other hand, is completely unhindered by copy effects, since it cares about what the underlying card that represents the creature is rather than the characteristics of the permanent itself. Turning a manifested creature into a copy of something doesn't change whether or not that creature can be turned face-up with manifest, nor does it change the cost required to do so.

Illusionary Mask is unaffected because nothing about it cares at all about the characteristics of the creature it caused to be face-down.

3) Its characteristics are those of whatever it copied, exactly the same as any other face-up permanent that has become a copy of something else.

4) Effectively, yes. As laid out in the answer to question 2, in order to turn a face-down permanent face-up, you check what the permanent's morph cost would be if it were face-up. If that permanent has become a copy of something that has morph (or megamorph), that means it would have that permanent's morph cost if it were face-up, so you can pay that morph cost to turn it face-up.