First Appearance: "Amazing Spider-Man" #13
Powers:  None, but he is a master of gadgetry and electronics, and he can create illusions as well as using a chemical gas to induce hallucinations.
Pros:  Mysterio has been part of Spider-Man's life about as long as he's existed in the Marvel universe.  A special effects wizard for film, Quentin Beck used his expertise to create equipment that would allow him to commit crimes, and over the course of his life (and afterlife) in various Spider-Man titles, Mysterio has had one of the strangest, most varied criminal careers.  There are several different character who have worn the "Mysterio" moniker, but Beck remains the best-known of them, and there's something exciting about a super-villain with no real powers who simply out-invents Peter Parker.  If it's true that the best villains in comics are the ones who provide a mirror image of some facet of the hero, then Mysterio is an essential member of Spidey's rogue's gallery, and it's about time he step forward to play a central role in one of the movies.
Cons:  Done wrong, Mysterio becomes the biggest Scooby-Doo bad guy of all time, where you have him doing miraculous things and tormenting Spider-Man with nearly godlike powers only to have it all uncovered as a fog machine, some blinking lights, and a voice synthesizer.  The films almost always try to pull off some sense of scale with the villains, and they may not want to do an entire film with Mysterio, who is admittedly a lesser-known bad guy than the ones we've seen in the film series so far.  He might work best in conjunction with another villain, and that way he could be played for fun and not have to be the biggest threat in the film.

- Drew McWeeny