I lowkey love your wereNeo thing but what if he meet the self insert? Cause i'm both scared or corius
Firstly I love this ask and I think its fun, but threw me in a bit of a conundrum because I don't remember ever making a self-insert for Deltarune. I've always understood self-insert as an fan character that's exhibitly meant to represent the artist/writer in the universe of the media and I haven't got one like that, but I narrowed it down to two of the most likely candidates.
So after this I came out thinking you most likely meant Byteraider (Darkner oc i made a while back for the uninitiated) and it just didn't cross my uncivilized mind that someone could use self-insert and fan character interchangeably :D Byte isn't representative of me as a person, he's just lab engineered to appeal to me specifically.
As to your actual question, I think I'd like to make a proper comic or illustration of what would happen if Neo met Byte since he'd fall into interesting grey area in Neo's targeting system. Byte never antagonized Spamton but he also couldn't do much for him after all the bad stuff happened so Spam probably didn't always think exclusively fondly of him.
But I also have a joke answer that I need to get out of my system first since I already filled the first half of this ask by unseriously trying to figure out which character you meant.