Demolition Derby rushed out of the gate once we created a design document that specified everything we wanted to accomplish and how we planned on achieving it. Unlike "race," which implies a set of rules that are universally familiar (cross the finish line first), "demolish" is more open to interpretation. We seized the opportunity to design a system that encouraged players to have fun by actively participating in the destruction, as opposed to avoiding it. For that, we needed the risk of being destroyed to pale sharply in comparison to the rewards of causing destruction.
Another early design choice was to create a secondary skill (besides ramming the opponent as fast as possible) that players could use to improve their performance both offensively and defensively. This became a jump button that allowed them to land on other cars inflicting massive damage, or to dodge cars hurtling in their direction.
With our goals firmly in mind, we cannibalized the same physics and camera engines we used for Free Realms racing, but implemented in an entirely different way. We made the cars more suitable for quick maneuvering, precise aiming, darting at the opponent, and leaping through the air. Additionally, we unlocked the vehicle's full range of movement, enabling it to flip and tumble for more visceral collisions and adrenaline-fueled moments.
While our arenas were created using a similar pipeline to the tracks in Kart Racing, we designed them around funneling players into certain sections where the most destruction would take place. We used halfpipes that took advantage of our physics to flip participants back into the mix, and ramps that allow them to boost directly into the most populated areas. I was the lead designer on the Snowhill Arena, and was in charge of power-up placement and AI control for all three tracks.