Hundreds of inventory items, each with properties that define exactly how it interacts with everything else in the world. Projectile weapons, jump pads, obstacles, explosives that vary in power and behavior, and ragdolls with their own individual response profiles. Make the ragdolls follow each other, attack each other, or run through whatever elaborate death machine you have assembled. The physics are the point. The outcome is rarely predictable, and that is exactly the appeal.