Cataclyst is a term for a Caster who was once considered a Natural, but turned Dark. It's also unknown whether they have the same powers and potential a Natural would. They are born from the Dark Fire.
In The Book of Moons there's a passage:
"The greatest of the darkness being the power closest to the world & the underworld, the cataclyst. The greatest of the light being the power closest to the world & the underworld, the natural. Where there is not one there cannot be the other, as without darkness there can be no light."
- Elemental Manipulation: Cataclysts are easily able to control the elements and the weather without hesitation. Their "go-to" element is fire and can start fires by accident called "The Wake of Fire."
- Time Control: They are able to control and freeze time, but it's very rare if they can.
- Reality Warping: They are able to manipulate reality at ease. So easy, even Sarafine was able to warp reality with Macon Ravenwood.
- Kelting: Kelting is extremely rare. Most Casters aren't seen to do it, only very powerful casters.
- Possession: They are able to possess other living beings and project themselves into the bodies of others.
- Dark Fire Control: They are able to control the Dark Fire in Darkborns and control their bodies.