Diamondhead is is about 7 feet in height. His body is composed of extremely sharp and durable crystals. In the Original Series his Omnitrix symbol is on the left of his chest.
In Alien Force and Ultimate Alien, Diamondhead's eyes have gone from yellow to green, and his body is now that similar to Chromastone, which is purple crystal which has black lines and dots over it. His head now has a purple hood design shaped to the size of it.
His species are made of a dense, hard green and purple crystals. So they had the ability to shoot shards and shaping their hands into weapons ( blade, knives etc).
He is able to manipulate the atomic structure of his crystalline structure and physiology at will, thus allowing him to make crude crystal weapons from any part of his body on demand and fire crystals rapidly from his hands. He can make huge clusters of crystals, creating crystal shields and make ramps. In certain ways, he can even reshape his projectiles into certain shapes and can make giant body parts like hands to capture enemies. The same ability also allows him to regenerate to a limited extent, such as re-growing or re-attaching severed or lost limbs. In addition to growing crystals on himself, he can also grow them over other objects. In addition, he is able making lasers and weapons similar to useless by refracting the beams.
In Alien Force, Diamondhead's powers have grown dramatically, as seen in the episode Vengeance of Vilgax: Part 2. Diamondhead can now levitate large crystal pillars.
In Vendetta, he is now shown to have another ability similar to Chromastone's energy absorption and projection abilities, he could absorb and redirect lasers and energy blasts, instead of refracting them in the original series.
Diamondhead is able to survive if shattered, as shown in The Secret of Chromastone when Tetrax broke him to get to Chromastone.