My guess about Dess is that her soul is wondering in the dark world, her body is in the light world, and her spirit is possessing her body trying to find ways to repair herself.

The body has skeleton-tied details (Gaster hands) and has armor resembling Papyrus. The only skeleton implied to be in the dark worlds, watching behind the tree. Clover (Dess’ stand in) likes trees (Papyrus is often behind the trees now), sports (Papyrus changes his outfit in Undertale to be cool and sports-themed), and boys. Oh yeah, the door to Papyrus’ room is actually decorated the same as Dess’ closet.

Dess’ spirit is actually somewhat disconnected and has its own form entirely. Knowing of its accursed state, it seeks completion and demands it.

So the Knight is a parallel between us and Kris. Where they will ultimately be divided by their own interest. And that’s the only way to beat them at the endgame.