I've often wondered if the river person is Napstablook. Blooky has the ability to be in two places at once, or at least to teleport, and he/she/it has the same voice as the river person. Of course, it may be just a generic voice for the game, since the person who likes your knock in Snowdin also has that voice. I suppose you could also argue Napstablook isn't cheerful enough to be the river person, but perhaps the anonymity of being under the hood gives him/her/it/them self-confidence. You never know.

What does everyone think about the stuff in Sans's secret room?

I was thinking The Nicecream guy is Flowey idk how O.O THIS IS A CRAZY THEORY XD I KNOW ASRIEL IS FLOWEY I JUST THOUGHT OF THIS AS A WEIRD THEORY O.O I just think it cause the eyes and The nice cream guy is Flowey acting nice and Nice cream is actually friendliness pellets. and you know how Flowey secretly follows you and The Nice cream guy is everywhere EXCEPT the ruins???!!!! WHAT IF FLOWEY IS DRESSED UP AS A TRAP!!!?? Idk this is a weird theory O.O