The demons in Prismordia arrived eons ago on a meteorite from ancient, abyssal space. Some say they are hiding from their true masters but it's pure speculation. When they arrived, they further corrupted the wounded fire god at the centre of the planet and now leech power from him. The diversity of their forms are pretty much infinite. There are greater and lesser types and they have varying motives and varying influence that are very abstract and not always evil. No one knows their true numbers but it appears they fight internally for dominion between each other quite often.

There was an age of dominion where they once ruled Prismordia, until the dragons came on another meteorite. The sea dragons and sky dragons pushed them to retreat into the planet's core from where they now sneak out on the occasions when their confidence is high. The dragons that pursued them into the core became corrupted by the wounded god and now breathe fire.

The biggest danger demons pose is to the sorcerers who attempt to study their language in an attempt to better identify and fight their corruption. In learning their language, they become very susceptible to demonic influence. Children who wander off into woods or caves are always in danger of being tricked by some kind of disguised imp too.

The are other elusive beings that arrived more recently who protect ordinary people from the demonic influence, but that's a whole other thing.