Thank you! I really appreciate you checking out the game.
For crouching, unfortunately I'm not quite knowledgeable enough with Godot yet to figure out that kind of thing, and I was really hurting for time, so I felt I had more important things to take care of with the game...
For the slide section, I am changing that in a small bug fix update, removing some mushrooms (as bouncing on multiple mushrooms at once is why your speed isn't carried over).