Exodermis

A old legend from those that jam deep into The Phlogiston claim to find a darkening rainbow ocean, a place where the ruins of a battle can be found, beyond, it is said one tumbles into another multiverse, the far realms. Upon some of these ships, strange 'eggs' were found, and brought back, these were the first Exodermis in recorded, understandable history. The creatures were learned to be related to aberrations of the far realms, but existed in opposition to most other aberrations.

The exact nature of them is unknown, one of the wilder theories are they an evolution of the Flumph, that have came back through time to oppose Illithids and other creatures of the Far Realms. Regardless, they have found local populations in various spheres, where they have formed colonies, and are often seen as close companions and valued members of mixed communities. Due to their communal natures, it is often that only one or two colonies exist in any planet, as they are more likely to join each other then work independently. (Note, this is also riffing on one of the creation legends of the Illithids in core, where they came back in time to create themselves.)

In Paraidisum

The Exodermis of Paradisium likewise came from a junction point between multiverses, in the deepest depths of the dungeon they were found admits research facilities with other alien creatures of other multiverses. One egg in particularly was born and joined with a host, a deep born succubus. Together, the two became a rare breeding pair, to create a new Paradisium Colony. There were other eggs that hatched into various known deviants, such as Consumption and Inferno.