Marvel have an embarrassment of riches as far as supervillains go, and while not every big Marvel movie has served up an iconic cinematic rendition (for every Loki, there's a couple of Malekiths), there are certainly some interesting, crowd-pleasing avenues for their future films to take.
A lot of this comes down to business politics and which movie studio owns the rights to which character, but whether they could appear in the Marvel Cinematic Universe, the X-Men or even the Fantastic Four, there's a plethora of indelible baddies who have yet to get their due on the big screen.
The cinematic potential is there, and though there's a laundry list of things that could go wrong. it's hard to deny that these iconic mainstays would sure entice both comic book fanboys and casual viewers alike.
Why He's Awesome: Mysterio has no superhuman abilities, but instead uses his special effects wizardry to create powerful weapons, illusions and tools of manipulation. He is also extremely skilled at hand-to-hand combat from his time as a stuntman, and his suit includes an iconic glass helmet, the ability to project 3D images to confuse Spider-Man, as well as various smokes that can lessen the Spidey sense, destroy webbing, and make the recipient hallucinate.
How Likely Is He?: Mysterio is a fairly goofy villain even for the standards of Spider-Man (but we love him for it), so would probably need the special effects guru backstory pared down quite a bit. It's been rumoured a ton in the past and is certainly possible, but not massively likely all the same. 3/10