Do you think every UT/DT character have a fell counterpart in the au or do you think some of them remain the same? Like fell jerry is identical to ut jerry or something 😭
SO IN MY HEAD AND MY VERSION.. THERE ARE DEFINITELY CHARACTERS THAT REMAIN " THE SAME" imagine it's the same character but slightly to the left.
The way I'm basing this imaginary chart (soon to be real) is by how closely involved they are with the presence of Gaster.
or if there can be an argument that they are involved.
(Friend, The secret bosses, his followers, eram, etc etc )
I perceive Gaster as an entity that exists beyond the narrative of a singular story (Universe). A guy who is and isn't there.
His presence only exists to those who really believe in him. or maybe want something from him? He decides when to show up if one isn't a believer (idk still working on this)
If a character is relatively close with Gaster and is a presence alongside him overseeing the narrative, It is likely they won't change. ( Friend, Eram, and maybe the egg guy).
However, if a character is relatively "close" to either Gaster or One of those presences and is a character within the narrative, they will have a few changes depending on how they interact with the AU versions of the characters in the story. ( Spamton with Tenna) ( Sans with Asgore)
I HOPE THIS MAKES SENSE, I know you said this for underfell jerry and I gave you a longer answer.
I can make UF Jerry identical to UT Jerry because I also think it would be funny if he stayed the same or was maybe a different color. maybe has a fur coat too because grillby took pity on him.