Ben is very excited to use his Grandpa Max's latest present, the Omnitrix! The Omnitrix is a glove that can turn its wearer into lots of different aliens. He puts on the Omnitrix and sees that there are still more alien forms for him to unlock. At that moment, Grandpa Max calls up warning Ben of evil being entering their dimension through some kind of portal. Sure enough, Vilgax has arrived at their home with plans to steal the Omnitrix for himself.
Ben transforms into Wildvine before he even realizes what he's doing and fights back against Vilgax along with his cousin Gwen and his friend Kevin. Vilgax manages to them all aside except for Alien X, who isn't interested in fighting and is about to leave when Vilgax attacks. Thinking quickly, Ben uses Alien X's powers to encase him inside a crystal block which he throws through the portal before it closes.
Ben suddenly Feels Something Different:
the Omnitrix is changing him! As Ben takes off running to get away from his family (he doesn't know what he's going to do yet), his mind races faster than his feet can carry him as new information floods into his brain via some kind of broadcast signal. This broadcast tells him how to use the Omnitrix and unlocks all of its previous functions along with several new ones. Once more feeling like himself and back home on Earth, Grandpa Max explains that the Omnitrix has scanned and analyzed the DNA of every living thing in the galaxy and locked it on to one...Ben's! It also suggests that by using xylene gas, Ben can change back into his human self.
Source: https://www.ben10gamesfree.info/game/ben-10-omnitrix-unleashed/
The next morning at school, Ben tries out all of the new functions he can think of (but doesn't reveal them yet to avoid awkwardness), but none work because it seems that while wearing the Omnitrix, Ben is only able to use his alien forms' powers while they are unlocked. Since Gwen still knows about her cousin's secret identity as a superhero, she suggests that he try putting on a pair of sunglasses during times when he wants to conceal his secret from prying eyes. He does so and for the remainder of the day, it works like a charm.
The next morning at school, Ben tries out all of the new functions he can think of (but doesn't reveal them yet to avoid awkwardness), but none work because it seems that while wearing the Omnitrix, Ben is only able to use his alien forms' powers while they are unlocked. Since Gwen still knows about her cousin's secret identity as a superhero, she suggests that he try putting on a pair of sunglasses during times when he wants to conceal his secret from prying eyes. He does so and for the remainder of the day, it works like a charm.
At home after school, Grandpa Max uses xylene gas in order to successfully turn back to humans from being a Tetramand. He then reveals that he is dying of an illness that no one knew about, but since he used the Omnitrix to turn into a younger version of himself, it seems his condition is healed completely and for good!
Unfortunately, even though the device successfully cured Max's wasting disease by reverting him back to his normal state (he originally became sick because he subconsciously prolonged his alien form to avoid leaving Ben alone at home), now Ben once again has become too dependent on using his future-given abilities in order to win battles quickly instead of properly training as Gwen does with Kevin.