Atasian

The Atasians (more commonly known as the Highbreed) believe that their DNA is the purest of all alien species, and seek to cleanse the galaxy of lower life forms.

History
They have travelled to Earth to exterminate mankind. The Highbreed Commander that usually fights Ben, insults him by calling Ben "scum" or even "filth". Also, during a fight with Ben, Ben actually bit the Highbreed Commander causing him to insult Ben by saying that he had infected him proving that they do think their DNA is the purest of all alien race. In the episode "Max Out", he attacks Max Tennyson, only to die when Max destroys the focus of the Null Void Projector and using it as a hand grenade. Their sizes come close to the sizes of Max and Vilgax. They make DNAliens do all their dirty work. The Highbreed are actually hyper-evolved plant life. This particular species had a very fierce belief in racial purity more so than certain humans that they reduced themselves to inbreeding which rendered them completely sterile and vulnerable to infection. In effect, the species was dying out and they wanted to take the rest of the universe with them until Ben used the DNA repair function of the Omnitrix to save them and, through the wise words of the Highbreed commander who was grateful when Ben repaired his arm, the Highbreed called off their attacks.

Abilities
The highbreed species possesses great physical strength and endurance and it was shown that they can even take on opponents twice their size like humongosaur, they also have the ability to shoot their fingertips like darts and quickly regenerate them, it has been shown that they can draw water from the ground using their tendrils from their abdominal area in the most arid areas.

Weaknesses
The Highbreed are extremely thermophobic and can't work in conditions that have high temperatures, although they don't appear to have physical weaknesses and are oddly capable of walking through fire unharmed, as seen in the episode "Grounded". However due to generations of inbreeding their immune systems are compromised which means that any form of simple diseases that "mutts" are immune to becomes a massive problem to the Highbreed. They also sport wings which they can use for flight.