B button should maybe be for another thing, like you can conserve candies to eat them with B but idk
Also I dont know much bout coding but I think Undertale also have a priority system (But UT has it to the vertical)
i believe undertale prioritized some particular direction, with the caveat of being weird (collision could cancel some directions, making it act weird near walls), MANTLE (the real one) has a priority system based on which button was pressed when, or at the very least the rest of deltarune does that, its entirely a visual thing with no gameplay impact but i think that if youre imitating something you should go all the way, unless there is a tangible benefit to not doing so
as for B button uses, look no further than having it be the interact button, since that seems to be notably missing and just happen automatically?