Can I just say, I HATE when people dismiss criticisms of "this part isn't replayable".
First of all, games should be replayed, because you don't fully appreciate them on a blind playthrough. You should always replay it to catch stuff you didn't notice and develop a deeper understanding of the story you enjoy.
Second, Deltarune was literally built with replayability in mind. The whole thing with the egg and shadow crystals especially. There's also options to skip large parts of the story-only segments and jump right into gameplay because the devs heavily accounted for people replaying the game.
Sure, Toby wants casual players to be able to get the best ending in one playthrough. But really, that's just an accessibility feature and obviously the "meat" of the game is in the optional content. You're always sort of encouraged to reload a save/restart a chapter and find shit you glossed over, that gives you more context to what's actually going on with the world
So when I say "this part sucks on replays" I DO think it's legitimate criticism, because the game is meant to be replayed, so replayability should be more seamless.