While browsing online, I stumbled across the Oracle page for Mistform Ultimus, and it got me curious. Why does the Ultimus keep its original wording, instead of changing its rules text to “Changeling”? Also, why does Mutavault, originally printed in the same set as Changeling, read “~ becomes a 2/2 creature with all creature types” instead of “~ becomes a 2/2 creature with Changeling”? In the case of Mutavault, changing that text to granting the ability instead of directly setting its subtypes wouldn't have any functional difference as far as I can tell, and in the case of Ultimus's rules text, there would be zero functional difference.

Edit: Answered my own question regarding Mutavault. Gains the ability in layer 6, but it needs to be applied in layer 4, so granting itself Changeling wouldn't work. Question about Ultimus still stands, though.

Edited Beau (Dec. 3, 2013 11:37:16 AM)

As a general rule, Oracle text is given to match printed text as closely as possible, so as to give the minimum amount of susprise to players who aren't aware of the Oracle wording. Mistform Ultimus wouldn't work differently today if it had Changeling instead of its current ability, but a card printed in the future might for example affect only creature with Changeling. If that happens, a functional change would be created. The current wording minimizes this kind of maintenance issue.

If Mutavault was giving itself Changeling, it wouldn't gain any creature types, since adding an ability happens in layer 6 while changing creature types happens in layer 4, i.e. it's too late for the Changeling ability to do anything.

Daniel Kitachewsky
L3, Paris, France
Rules NetRep