Mysterio is a tricky one, I'd put him on the cusp of A-list. It's an iconic design, but that's because it's rather silly looking. He can be a considerable threat,(he was the inaugural villain when Ben Reilly first took over as Spider-Man) but his most dastardly deeds were in other character's titles (Daredevil, and tricking Old Man Logan into murdering the X-Men). I think if he appears in the next movie (and is well received) I'd move him into A-lister tier.