• Ralsei dies permanently and is replaced by Noelle in the party. Reason: Noelle needs more screentime, and killing Ralsei off would be a great twist without being an asspull
• Papyrus shows up for the festival. Reason: It's the most likely moment for him to go outside
• Eram is further established as the defier of the prophecy (possibly being the one who kills Ralsei). Reason: Ralsei was scared of Northernlights in Chapter 3 because the prophecy didn't talk about ir
• Gaster gets further focus. Reason: he's clearly going to be important and casual fans must be introduced to him
• The internet comes back, unlocking a Spamton superbossfight. Reason: it'd be so awesome, it'd be so cool
• We get a character who's similar to Tenna, but evil. Reason: there's a TV in Asgore's house, and a playtester said they wanted to say the opposite of "I love TV"
• Chapter 5 begins in Noelle's body if you did the weird route. Reason: We see Noelle developing a new soul in Chapter 4's weird route

Give me your predictions too. Not the "safe" milquetoast ones. I'm speaking really unhinged ideas that you think would fit in the narrative