The source code is up on the jam site at the link, so you can see all the details.
I have a state machine for the spring behavior. Landing, Falling, Rising, etc. Look for the Tween actions take on state switch. The size change is handled by the new Z elevation feature. The state switch is time-based with a different period/spring (all based on instance variables.) There's a master 'Spring' with location and direction and Child 'SpringRings'. The player is a special instance of the Springs and has 8-way control enabled.
Hope it's useful, looking forward to seeing your game.