Yes, I'm late. Anyway, shooting out some notes of varying lengths. Untagged spoilers below! How would I make this thread otherwise!
First off wow is Tenna hard to put up with. Which is to say he's a great character. How desperately he clings to a past and brings it up in the most awkward/painful ways for Kris knocked the themes out of the park. Also I won't forgive Deltarune fans for how quickly the M/M pairing took over. Throw crumbs at the fujos and they overwhelm overnight.
The difference between Tenna's boards and the original game they're built from make a beautiful allegory for Toby Fox's game design. Ramb laments the new boards for being "streamlined" and talks about the "freedom" of the original game. But when you start playing it, you find out pretty quickly there's no freedom of choice. You just Proceed on a single path the game expects you to figure out. Meanwhile, Tenna's boards are heavily scripted, but offer plenty of variety. Of course, Deltarune offers both of these in a few different ways so that Toby will always come out on top. But it should be stated that the original game is directly built off of the action and RPG titles that Toby ruthlessly critiques in his works.
Raise Up Your Bat having lyrics that get changed on the fly while you're focusing on the notes is probably the best troll in the game so far.
The Roaring Knight is tough and ate my revive items. Certainly the hardest encounter so far, but still a mile or so away from Sans territory.
Carol's short curt sentences mean most of the words she says are capitalized for the few lines she gets. That, with the blue and the secret trucies with Kris point to some similarities with Queen. Queen likes Kris because they're "chill," which is to say they go along with her plans and don't upstage her. And it's troubling to find something Kris has in common with their dad.
Speaking of Asgore, I expect to see more of him in Chapter 5 what with that line about a garden. Dude loves gardens. But he's not going to light anything up. My guess on that has to be Rudy. Picture this: You're in the hospital. Life at home is getting tough for your daughter because you aren't there to balance out your wife's more abrasive qualities. And then your best friend from college, who's already tanked his own marriage, becomes the de facto man of your house during your recovery. Rudy is fighting for his life while Asgore tends to his wife's bushes. That'd piss any red-blooded deer off.
Gerson calling Susie the dragon is cause for note. Dragons are powerful, with that power varying based on the media. One piece of media I know Deltarune takes inspiration from is Mother 3. In Mother 3, there's a dragon that destroys and rebuilds the entire world. Fits the whole "fighting to change fate" thing Susie has going. Also between the dragon thing, her love of red stuff, and general disinterest with "girly" stuff, Susie has a bit of Terezi DNA going on.
Magic is FAKE AS SHIT/FUCKING REAL