Unfortunately, we cannot help you make a whole system.
At most I can give advice on this aspect of the looping system which is aligning the character to the surface normal like in a loop motion, this is a whole problem in itself.
Video:
Possible Orientation method 1:
Now for the movement you need to somehow create a character controller that
Disables gravity
Creates a force/movement to stick you onto the loop (get Raycast normal in a lot of directions?)
Create the camera change which goes alongside with the control scheme, never played a sonic game recently so I cannot help you with the controls here.
Make the movement force perpendicular to the slopes floor
For getting a direction movement vector perpendicular to the slope perhaps you can use this cross product technique:
