It might just be me who tries too see a connection that doesnt exist. Anyways, in the caves where you can go from the forest to a backalley of castletown, there is a puddle of water, and when you interact with it Yoki says something like "This water is too muddy to heal anyone". I think that might reference Undyne getting water from Frisk in hotland. Might be a bit farfetched, but yaknow, it's only a guess.