Hi! From what I know, Kristal is an engine for deltarune battles only, so the answer is no.
I'm sure it is possible with a bit of a workaround to create an undertale-style battle, but what would be the point of doing it if CYF already does it? Besides, CYF recently got an update, version 0.6.6, which adds a lot of new things that will help me add new features to the game