Propeller spheres

Propeller Spheres are flying enemies from Nitrome's main game, the glassworks.

Appearance
The spheres appear as an orange, robotic ball with some sort of glass panel on its front, and a propeller on its top, with which it flies.

Game Information
The spheres patrol back and forth in the air along horizontal or vertical routes. Some are on the front side of the glass, others are on the back. They can be defeated by hitting them from the other side of the glass. They appear from level 3 and onwards.