Board Thread:Questions and Answers/@comment-25413416-20140917223744/@comment-24152851-20140918013820

I doubt he's energy, my guess he's composed of darkmatter or something other than the normal matter which the visible universe is made of. Perhaps something extra dimensional which is why they possess powers that seem omnipotent. The Omnitrix can only hold DNA of creatures that are matter, or in the case of NRG and Echo-Echo partially composed of matter.

I never got the "energy beings" thing, and how energy beings are also able to have a solid form. But regardless he seems pretty solid to me. Energy beings are shown to pulse and have an unstable form (anodites hair always flows, or NRG's true form is just electricity), but Alien-X is solid enough so that Kevin can pick him up and put him in the car.