In his own words, Spidey was "the dude that kicks ass online, and kills terrorist, the rumors that I am a secret agent armed with top secret weapons. Well, I don't, though I do kick lots of terrorist ass, and I have some pretty cool powers (and weapons)." He had a secret identity and a girlfriend named Quistis (but it's okay if he uses her name, because she's from another planet).
After receiving a mysterious letter from Master Hand, a boss from the Super Smash Bros. games, he decided to attempt to become one of the Smashers. He traveled by means of robotic limousine to the starship Great Fox, which picked up a few more prospective Smashers (including Harry Potter) before dropping them all off at Smash Mansion, a place that does not exist in canon. By means of a simulation, Spidey proved himself in single combat with Wario, verbally abusing him the whole time, and became the first new Smasher.
Spidey's "cool powers" include the use of spells from the Final Fantasy continuum.
Spidey3000 was charged by Agent Earwig as follows: "Spidey3000, I hereby charge you with definitely being an author-insert and a Gary Stu, and I further charge you with crimes against the Super Smash Brothers continuum. Specifically, with employing silly text dividers that sound like ghosts; with lots and lots of spelling, punctuation, and grammar errors; with using bad logic on several counts; with causing time-space compression and making my partner be sick; with giving yourself special powers that you shouldn't be able to have, claiming to be a legend without any real justification, and having an ego that spans worlds; with throwing pretty much everyone from SSB so out of character that our CAD would probably explode if we tried to use it on them; with abducting canon characters from other universes, such as Harry Potter; and with making up uncanonical offspring of canon characters, meaning Larry and George there. And I don't even know about that other guy you mentioned, because he didn't do anything."
It should be noted that Earwig ad-libbed the whole thing because he couldn't read Derik's writing.
Having charged Spidey for his numerous crimes against good writing, common sense, and the SSB canon (not to mention abducting Harry Potter), Agents Derik and Earwig were on the point of killing him when his own author appeared and blew the Stu's head off with a shotgun. As it turned out, Spidey3000-the-author had learned the error of his ways some time before the PPC got wind of the badfic and was eager to help out.