Atomic-X's torso is mainly that of Atomix's, but is Alien X's height and shape. His head is in the shape of Alien X's, with Atomix's eyebrows fused with the middle spike of Alien X's head, and the details from Atomix's chin. His upper body is the shape of Alien X's with details from Atomix. His lower arms are that of Atomix, while his hands have the coloration of Alien X. He has Atomix's belt while it lacks the green, and his legs are that of Alien X with details from Atomix. He wears the Biomnitrix on his chest.
In the original artwork, his chin has Alien X's starfield design. His belt is white, and breaks in the middle of his waist, as his chest arrow is longer. The second rings on his lower legs are white instead of green. Instead of a green metal collar around his neck, he has a white v-neck pattern with green bolts at the sides, and his boots are only white on the front of feet, rather than entirely so. The Omnitrix is not on his chest (actually, it is not visible anywhere), with Atomix's energy chest symbol in its place.