In his armor, his feet are hooved. He has purple pads covering his central joints, an alien like belt, and four central lines to provide outlines for his face, which are his eyes and mouth. When his black and pink mask is broken, it reveals an ugly, mutant, gray-yellow creature with pink and gray robotic eyes and four arms. He is somewhat similar to a predator from the Alien vs. Predator franchise, as most predators wear masks to hide their faces.
In Omniverse, his appearance hasn't changed much. his jumpsuit is now a much more reddish color, with the black highlights now a dark blue, and the silver armor plating has a blue tint to them too. Most of his pouches are smaller and the ones on his shoulders are no longer sunken in.
Sixsix first appeared in the episode Hunted, where he along with his rivals Tetrax and Kraab were to take the Omnitrix from Ben and give it to Vilgax for the reward, but he and Kraab defeated by Grey Matter.
In Ben 10: Secret of the Omnitrix, Sixsix was a prisoner on Incarcecon, then became Vilgax's helper. His mask was broken completely, revealing that Sixsix is an ugly, mutant-like, light gray creature with robotic eyes. Sixsix was defeated by a great source of feedback from the Omnitrix.
Sixsix has purple armor that has pouches which contains weapons like machine guns, little guns, twin blasters, laser discs, buzz saws, an energy chainsaw, a laser blade, a laser gun, a whip, a sonic weapon, grenades, rockets and some mounted laser guns coming out of his jetpack. He has a radar that can track the Omnitrix when it is activated. He also has little arms that are used to throw the pikes and grenades when using his blasters.