Thanks for great feedback ! please let me answer this real quick
1. point number 1, 2, and 4 I`m already aware.
2. for point number 4, in the prototype I used a square collider, then when I was working on the art, I changed to a rectangle. So when I changed that in the prefab, the bottom collider went inside the stage.
3. for point number 3, I actually prefer 3D because the character controller is very comforting for me. So when I switch rigidbody, I don't know how to fix that. I already used fixedupdate but it's the same.
4. for point number 5, When you knock the slime out of the stage, it walks towards you from behind the crystal. I'm not applying any specific state in order to activate the crystal. So, my bad i guess.
Again, thanks for the great feedback !