Board Thread:General Discussion/@comment-5537927-20130419114943/@comment-3974711-20130419135522

It's cool. Diamondhead proved to be crucial when we were introduced to Tetrax. Diamondhead left shards of his crystal behind, which Tetrax noticed, alerting him to the Omnitrix user being in the area. (I don't think he suspected another Petrosapien, as Vilgax had kaboomed their planet already. Therefore, it had to have been someone with access to their DNA.)

Also Cannonbolt fits pretty well in his first appearance. If it were Diamondhead introduced as the new alien, Ben wouldn't have learned to not judge his forms simply for having a lame power (compared to the rest).