I can't see the Knight being anyone but Dess, honestly. The antlers narrow it down to the Holidays, but Noelle is Noelle, Rudy is 100% fucking dying by next chapter, and Carol is too old to be doing what the Knight does. I mean, folding their arms while levitating up a staircase, doing the finger point, that one sword summoning animation that turns a bat looking object into a sword, stuff like that. Hags do NOT move like that, and the Knight is too fucked up looking to be a normal Lightner.