Iknow that everyone believes that the riverpersons message about “beware the oen who speaks in hands” could be about gaster because wingings uses hands for some letters but I don’t think that’s who they were talking about

It’s alphys. You meet the river person right before getting in alphys’s lab and during the mettaton quiz show,

I think the riverperson was warning frisk not to trust alphys because alphys was the one who planned out everything in hotland and made flowey and is generally someone who fucked up a lot