Do you want them as items/weapons?
(Dramatic voice) Playertypes.
I'd prefer if they wouldn't jump and had a max speed of ~60 studs per second
Also if possible three variants, one slippery (light), one less slippery (normal), and one even less slippery (heavy)
Edit: A simple blank marble would be cool but if you could make a cat's eye whose colors are dependent player's torso n stuff that'd be tubular also.