They are transparent balls with some sort of elusive glowy liquid sloshing around inside. They come in 3 colors: purple, orange, and green.
All these enemies do is bounce around the screen indefinitely. They have very similar movement properties to fireballs, except their bouncing is much, much floatier. They are also immune to bottomless pits.
Every sphere takes one hit to kill. It's probably best just to avoid them though, as timing a jump on them can sometimes be difficult. So, it wouldn't hurt to have a helmet like Maniaxe who can dispose of Spheres from afar, just in case.
Spheres are encountered in the following levels:
|Bloody Swamp||Skydragon Castle 1||Elsewhere 22|
|Elsewhere 5||The Deadly Skyscrapers|
|Hidden Canyon||The Nightmare Peaks 1|
|Stairway to Oblivion|
|Wind Castles 2|
Analyzing enemy data through a VDP viewer reveals what appear to be unused laser sprites accompanying the Sphere. Since they are oriented down, diagonal down, and horizontally, this shows spheres may have exhibited the same attack protocol as Clouds at some point in development.