The bumbleball is a new Portal 2 puzzle element created by Skotty and Moth of Team Citruz.
If the bumbleball is outside of the players view it will bounce around every 2 seconds, making a distinctive sound when bouncing. They're *very* different to spheres, and behave differently to blue painted cubes, making them unique in this respect.
More information is available at this link: 
The download contains:
-A normal sphere button specialized for the bumbleballs, not useable with other objects.
-the single bumbleball (model and textures)
-droppers for bumbleballs, dirty and clean
-the .PSD file for custom textures
bumbleball supports up to 16 skins -- 'skin' values 0-15 in Hammer
No scripting is required to add a bumbleball to your map; just add one of the included dropper instances, and trigger it with a button.
- For dissolving a bumbleball (for example in toxic water) you have to FireUser4
- Paint will colour the bumbleball, but because it's a normal prop_physics, it won't jump or glide. The use of a prop_physics_paintable fixes that problem, but the ball won't be visibly painted.