Chapter 5 takes place in the hospital
Asgore opens the fountain with the black shard
The flower trapped in asylum is the one in rudy's room
Dark world rudy is him at his prime
Noelle gets to spend plenty of time with rudy
The twist is that dark world rudy is secretly a dustner, rudy died right before the fountain was opened
Asgore is revealed to be a bad guy
Knight identity is revealed

The shadow crystal boss is berdly, and only accessible on weird route. Getting the crystal kills him.