[TippetsTX]

Has anyone here developed any campaign history for the Mnoren and Cidri? Specifically, does Cidri have any special purpose?

One idea I like would explain why the Mnoren created Cidri... it's a prison. At some point in their long history of dimension-hopping, a renegade or perhaps overly curious Mnoren traveled somewhere that they shouldn't have and inadvertently punched a hole into a dimension of pure chaos and evil. The entities (i.e. demons) inhabiting this plane sought to escape and invade the home reality of the Mnoren so in response to the threat of destruction as well as the guilt of having caused the issue in the first place, the Mnoren pooled their resources to create a massive artificial planet that is actually a powerful dimensional containment device surrounding the breach.