{1}: Mutavault becomes a 2/2 creature with all creature types until end of turn. It's still a land. Some changelings born at Velis Vel never return, but their essence never leaves.
Illus. Fred Fields
4/1/2008: Although Mutavault has all creature types while it's animated, it does not have the changeling keyword ability.
8/1/2008: A noncreature permanent that turns into a creature is subject to the "summoning sickness" rule: It can only attack, and its {T} abilities can only be activated, if its controller has continuously controlled that permanent since the beginning of his or her most recent turn.