The character designs could blend in interesting ways. Take Alice Angel from Batim. She could be given a more Undertale - inspired dress. Instead of her normal white dress, it could be a dress with a pattern that resembles the Delta Rune. Her halo could also be a different color, like purple, which is a color often associated with magic in Undertale. On the other hand, Toriel from Undertale could be depicted in a more 'inky' form if she were in the Batim world. Her fur could have a wet - ink look, and her robes could be tattered like the clothes of the characters in Batim who have been through a lot in the studio.