Maybe reuse some ball materials from WaDF2? That way they would actually get into a proper game, like the electric ball, magnetic ball and hover ball?
I suppose a glass ball would be anyone's thrill...
If you're looking for new materials, then I would aim for certain abilities, like:
- floatation on water surfaces;
- helium filled that will be unable to move in downwards direction, so once you select this, you will rise and rise... like a balloon;
- momentum ball - has little movement abilities, but once you hit jump or perhaps even the slow button, it will not respond to your controls. instead it will continue moving into whichever direction it moves until you release the button, or perhaps to give it an element of gameplay, once you hit a wall it also stops.
- ball(s) that becomes solid to certain lightbeams, but anything else goes through it. This could be a great puzzle element like in
Utopioca