Just letting you know that Kristal has a library for Undertale battles. It's called Magical Glass Redux.
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Hey there! Sorry, didn't see your reply.
Anyway, thank you very much for the help. You're right, Kristal has evolved quite a bit and there are now a bunch of new libraries like Magical Glass, though I already have abandoned CYF and have made my own engine now, so it would be really unproductive for me to restart everything from the grounds up again