|this all speculation when more info comes out thing will change|
Shifty is about the same as they were in Storyshift. Shifty is just a bit taller, they also wearing a jacket like Chara and a rainbow scarf, Shifty can also use DT magic. They are being taunted by Mettacrit to reset.
Napstablook has dreams about turning into Boogie. He finds out that Mettacrit is doing something to Shifty.
Not much is known about them. They are trying to force a reset out of Shifty so they can "fix the mess that Shifty made."
Shifty: she doesn't speak human only wingdings since the fall broke her voice box.
Chara teleported him and Shifty there on accident
sans asks Asgore if he could have a another son to be happy and he created Gaster