Xylene

Xylene is the alien who sent the Omnitrix to Earth for Max to find. Although she is not shown until later, her ship is seen in the first episode fighting off Vilgax and launching the Omnitrix to Earth before her ship is destroyed.

Xylene first meets Ben and Gwen when they at the park. They think Xylene is a villain, but then, Grandpa Max arrives and stops them. Xylene recognises Max and stays in the Rustbucket for a while. When Ben and Gwen first meet Xylene, they do not like her because she is living in the Rustbucket with them and they have only had a short time with Max

Abillities
Xylene has two known abilities, the first, is being able to use her green hair like a tentacle, which can be used as an offensive weapon to fight off enemies. The second is using a pink force beam from her third eye, which she uses in the battle with the second of Vilgax's battle droids to release a container in the port/docks.

Xylene is also shown to possess great knowledge of the Omnitrix, having since being the one who sent it to Earth. This knowledge is demonstrated by manually choosing which alien to be activated.

Weaknesses
Xylene's main weakness is her lack of combat skills, but she more than makes up for this with her intelligence.

More about Xylene
Xylene is the one who sent the omnitrix to earth for Max Tennyson to find but unbeknown to her, Ben was the one who found the omnitrix.