Forge and Crucible
As part of one of my earliest prototyping efforts, I was tasked with creating a platformer controller that would be similar to something like Super Monkey Ball, and other 3D platformers with idiosyncratic movement. The initial tests I did with the ball movement was some of the most fun I've had creating something, since it was largely a dance in figuring out when the player should be given more or less control.
It took a lot of re-working of the Unity physics system before I created something with the right amount of controllability; including heavily constraining object rotation while adjusting the mass of the rigid body until it felt like the player was rolling around without throwing off the directional vectors used.