From Sonic Retro
It's a Kiki driving a Kart, which comes in may different colours (green, light and dark blue, pink, red and black) and attacks by ramming its car at enemies. They show up first at the beginning of Twinkle Park for Sonic, and the destroying of at least one is required. It will leave its Kart behind, allowing Sonic to hope inside and run down Twinkle Circuit with it, where they also make an appearance. If a Kart Kiki hits the sides of Sonic in a Kart, it hurts him, but if Sonic rams them with the front of his own Kart, they will be destroyed. They oddly do not release an animal when destroyed unlike the Cop Speeder.
They have another model which uses police karts instead of colour ones, the Cop Speeder.