Metamorphs, formerly known as changelings when they were first discovered, are a second-tier ascension focused upon Change Magic. They are creatures of pure chaos, and will not revert to any particular form when exposed to raw Change, even if they possess another ascension. Their natural form tends to be a puddle of silvery ooze, but this is merely a prefered neutral form, as they're beings of primal chaos.
Becoming a metamorph is a dangerous business, and most die in the attempt. Most metamorphs were created by accident. Exposure to extremely high levels of Change is necessary, but one must also be attempting to Change during exposure, and thereby embrace the chaos. Most of the time, if this is intentional especially, the person simply dies or is horribly mutated. Even if one manages the ascension, if one doesn't also possess some Change Magic of their own, they will very probably lose the ascention upon rebirth. Metamorphs also almost always go insane at some point.
Metamorphs are notoriously difficult to actually kill, however. Wounds that would injure or maim any normal being merely pass through a changeling like water. Even decapitation or dismemberment won't stop them, as they are still capable of controlling each part of their body so long as their mind is still active. They can easily take on any form, small or large, and even separate parts of their body from themselves to conjure things. Generating matter tends to tire them out quickly, however, requiring them to rest or draw energy from something.
But a metamorph's most feared ability is the power to absorb other beings and control their souls in that manner, thus gaining their powers, much like a demon soulbonding someone. Unlike a demon, the person's soul is trapped within the changeling's body. If the changeling is a skilled enough telepath, they tend to make their souls unaware. If they absorb a telepath without that skill themselves, though, the telepath tends to take over. Much like a demon binding the soul of a person, people bound in such way to a metamorph will become metamorphs themselves if separated from the ooze. Most of the time, such secondary metamorphs do not retain their powers over rebirth.