He first appeared in My gigantic camping trip .
Like he has been mentioned for infamously doing, Stewart is able to chat until sundown has arrived and never stops talking to the point where he uses words from the dictionary that he had read during a period of silent at school. *Most of the time*
Last summer vacation, he continously talked to Cassie at the Amusement park to the point of getting a sore throat. He will talk to ANYTHING including their golden retriever Max. It is unknown if he can read Alien text like his relative Cassie who wields the Omnidewtrix.
It is known he can absorb abilities as second main species Absorbenites have been explained to do, but it is not known if he is aware of his own abilities after the events of 'My gigantic camping trip'.