You should begin with a clear idea of what makes your Undertale AU different. Develop interesting character backstories and interactions. And make sure the dialogue is engaging and fits the tone of the comic.
Well, they might see different versions of characters from Undertale. For example, the RWBY characters could be really surprised by the unique battle mechanics in Undertale's AU multiverse. Maybe Ruby would be especially interested in the different types of weapons or magic used in that world.
Blake could also be a great character to focus on. Given her own complex backstory and her tendency to be more introspective, she might have deeper insights into the characters and situations in the Undertale AUs. She could form unique relationships with some of the more morally ambiguous characters in the Undertale multiverse.
An AU fanfic is a type of fan fiction where the story takes place in an alternate universe with different settings or circumstances than the original work.
An au fanfic is a type of fan-written story that takes the characters or setting of an existing work and places them in an alternate universe or situation that differs from the original.
Well, if Undertale could watch Undertale fanfiction, it could lead to some chaos. For example, Sans might make jokes about the wild scenarios in the fanfics. Papyrus, on the other hand, might be eager to correct any misinformation about himself. And Flowey could use it as a way to manipulate things further, seeing how the fans view the characters and using that knowledge to his advantage in this strange, meta - situation.
Some characters might be amused. For example, Sans would probably make some witty remarks about the fanfiction's plot twists. Papyrus, on the other hand, might be a bit confused at first but then get really excited if he finds a heroic role for himself in the fanfiction.
In fanfiction, 'au' is short for 'alternate universe'. It allows fans to explore different 'what - if' scenarios. For instance, in a Supernatural AU, the characters could be normal humans instead of hunters. Writers can change character relationships, like Sam and Dean being estranged instead of the close brothers they are in the original show. It gives a lot of creative freedom to play around with the source material in new and exciting ways.
For Belle, as a barmaid, she could be developed as having a more street - smart side. She has to deal with all kinds of customers, so she becomes tougher and more resourceful. The Beast, in this AU, could start off as more withdrawn and bitter. His encounters with Belle at the tavern gradually soften him. He could learn about human kindness and humor from observing the interactions in the tavern.