What is the effect of the Dragon Ball?

Solution 1:

The Challenge Level on Level 73 uses the Dragon Ball as its weapon. I used this floor as an ample way to test the weapon in every conceivable way possible.

This led to the conclusion that it's just a slow moving ball of purple energy. It can neither pass through walls or enemies, it has a very slow rate of fire, and it only has 15 ammo. There are a plethora of better long range weapons available, and while its damage is decent (able to destroy Mini Octobosses in one hit), its downsides are just too hindering to make it that much of a viable weapon. The slow rate of fire makes it unsuitable for tough enemies, while the very poor ammo count makes it unsuitable for weak enemies.