I couldn't find the answer to this but what happens if you have a face down morph on the field and someone plays Ixidron? Does my morph creature stay face down or do they get turned up?
The text printed on the Ixidron reads as follows:
As Ixidron enters the battlefield, turn all other nontoken creatures face down. (They're 2/2 creatures.) Ixidron's power and toughness are each equal to the number of face-down creatures on the battlefield.
As morphed creatures are already face-down they are unaffected.
This is reflected in the Ruling made in 2006:
2006-09-25 : Turning a face-down creature face-down typically has no effect; the creature’s status is unchanged.