Honestly
Dess or Carol being the knight makes sense to me
There's a lot of suspicion that Gaster is gonna show up in deltarune and the markings on the Kight's hands could imply their connected to him somehow, so maybe one of them made a deal with him
Unless Gaster straight up is the knight in which case screw it all
Dess is just dead, Carol has the sword in the house for no reason other than to throw people off, and Papyrus just stays home on his computer all day and that's why we don't see him