Octoball
From Inkipedia, the Splatoon wiki
Octoballs are Octarian fighters who roll around and spread Octarian Ink as they roll around. Attempting to shoot Octoballs with your ink causes them to start rolling in the oppostie direction. However, if you submerge them in a puddle of your own ink, then they sink in and can be splatted.
Appearance
Octoballs are round spheres with one green eye, and huge lips. They have small boots.