Diamondhead

Diamondhead (voiced by Jim Ward) is a Petrosapien alien the planet Petropia.

Ben first transforms into Diamondhead in And Then There Were 10 to fight an alien robot sent by Vilgax.

On Kevin, he is voiced by Charlie Schlatter. On Gwen, she is voiced by Vanessa Marshall.

Abilities
Diamondhead's body is composed of an extremely dense and durable organic crystal, making him nearly invulnerable. Diamondhead can manipulate the atomic structure of his his diamond physiology at will, allowing him to create crude crystal weapons from any part his body on demand or fire crystal shards from his hands. In certain ways, he can reshape his projectiles into certain shapes. He can even control those that are not connected to his body. This same ability also allows him to regenerate to an extent, such as regrowing lost limbs. In addition to growing crystal from himself, Diamondhead can grow crystal over other objects. Lasers and other similar weapons are useless against Diamondhead, as his crystal body acts as a prism, refracting the beams. The one drawback to Diamondhead's crystal form is the crystal itself, which can shatter if exposed to sufficiently strong sonic vibrations. Though his diamond structure is durable, it can be damaged with sufficient force. While Petrosapiens can regenerate limbs, there is a limit to how much damage they can recover from.

Race Against Time
Diamondhead (voiced by Daran Norris) made an appearance in Ben 10: Race Against Time, fighting Eon. Unfortunately, Eon got away so Ben spent his remaining time as diamondhead in the girls' toilet.

Alien Force
Diamondhead (voiced by Dee Bradley Baker) makes an appearance in the third season premiere of Alien Force, regenerating from Chromastone's remains after Vilgax destroyed him. Diamondhead's appearance is slightly altered, with a primarily dark blue uniform that also covers part of his head ( However, all petrosapiens have this natural "costume". It wasn't seen before since ben's clothing covered over it). In this series, his crystals can explode and he demonstrates the ability to psychokinetically control the crystal he in Ben 10: Alien Force creates.

Diamondhead's body is different in that his Omnitrix symbol is now in his chest and his eyes are now green. He also has a similar body structure to the one of Chromastone, a related species. In the episode The Secret of Chromastone all Petrosapiens have a dark purple body (in the original series we never saw that because both Ben, Tetrax and all the Petrosapiens were wearing clothes). Ben transforms into Diamondhead after Vilgax destroys Chromastone's body (seemingly killing Ben in the process, but the crystals that made up Chromastone re-constituded into Diamondhead, giving Ben access to this form once again. As Diamondhead, Ben states "You're in trouble Vilgax, I've had a lot of pratice with this one.", indicating Diamondhead is one of the alien forms that he had a lot of experience with (this maybe in reference to a scene from an episode of the original series, in which a young Ben can be seen training in this form under the guidance of Grandpa Max), possibly due to it being one of his original 10 alien forms. Ben proves this by using it to literally crushing Vilgax (under three giant chunks of crystal), forcing the villian to yield defeat. Ben's use of Diamondhead to defeat Vilgax is ironic since he is the one ultimately responsible for the destruction of Petropia.

Diamondhead is now once again selectable in the Omnitrix. Ben briefly transforms into Diamondhead in the episode Single-Handed after becoming trapped in the Null-Void after he is dimensionally displaced from his left hand (the hand that wears the Omnitrix) by the bounty hunter Sunder. This saves Ben's girlfriend Julie Yamamoto from Sunder, while she is trying to protect Ben's left-hand & Omnitrix. Ben's dimensionally displaced hand protects Julie by firing Diamondhead's crystal shards. However, this causes problems for Diamondhead, as his left arm also fires shards, unintentionally destroying a rock bridge he was walking on. Diamondhead also appeared in the episode In Charms Way, fighting a hypnotized Kevin. Diamondhead also appears in The Secret of Chromastone by releasing Sugilite inside him, where he saves his home planet Petropia with the a crystal Vilgax had that can regenerate Petropia and there species. Since he is seen as a hologram in the while Albedo is looking through the prototype Ultimatrix he will be in Ben 10: Ultimate Alien

=Ben 10,000=

Future Diamondhead has regained predominant clothing. As well as a black-layered shirt, the Omnitrix symbol has moved to the center of his chest from the left side of his chest. His pants are now white and he has black boots, and his jaw also seems jagged.

=Homeplanet=

Diamondhead’s home planet is Petropia. It was destroyed by Vilgax some time ago when Tetrax was under his influence. Apparently, the people prepared themselves for things like this and created a guardian called Sugilite. The crystal that was used to destroy this planet ironicly help restore it back to life.

For more information on this planetsee: Petropia.

Trivia

 * In the German version of the series, Diamondhead - like so many others of Ben's aliens - was for unknown reasons misnamed. In his case he was called "Stahlschädel" ("Steel Skull"), even though he is evidently composed of a crystalline substance.
 * In the episode Vendetta it was shown that Diamondhead absorbed Ragnarok's energy blast and rederected it like Chromastone.