Consider what ziggo (https://www.youtube.com/watch?v=OuyG3FmixRI) could do as a lightweight. Now make it 100kg with tungsten teeth instead of steel and two counter-rotating hemispheres to cancel out the torque and let it turn on a dime. Put gear teeth on the inside of the shell and run multiple drive motors so that you can rev it up to full speed within the first few seconds of the match and then switch off drive motors as necessary to save power. With a heavyweight bot you have a big weight budget for powerful batteries and motors so I think you could fit several kilowatts of power for both the drive system and the wheels, which are important for a spinner since you need quick acceleration to outmaneuver your opponent and attack its weakest point. To protect from getting flipped, you could design the tooth lowest to the ground to be on a horizontal hinge with a linear actuator running through a hole in the shell, so that during the match you can lower it to the necessary angle to hit anything trying to slip underneath.
Napkin math: A 25kg shell, 1 meter diameter, spinning at 1000 rpm has about 17 kJ of rotational kinetic energy, (roughly equivalent to a .50 BMG bullet) so several kilowatts of power for a few seconds should be enough to rev up fully if friction is kept sufficiently low.