Backstory: The Lizard, AKA Dr Curt Connors, has been troubling Spider-Man in comic form since 1963. Connors was a gifted army surgeon who became obsessed with harnessing the power of reptilian limb regeneration after his own arm was injured (and subsequently amputated) in a blast.
After extracting some DNA and experimenting on a rabbit, Connors foolishly tested the compound on himself, and was transformed into a hulking reptile-man. Peter Parker did help to find a cure, but various triggers brought out the return of The Lizard over the years. If Ifans Played Him: Curt Connors would likely be as slippery and sinister as his (probably CGI) cold-blooded alter ego. Spidey-Sense Tingling? This has got to be one of the most likely routes that the reboot'll go down. Ifans would be well-suited to the charismatic doc and The Lizard would be a great physical match for Spidey.
Throw in the fact that Connors was tipped to be the villain in Sam Raimi's abandoned Spider-Man 4 (Dylan Baker played the Connors in parts 2 and 3), and you've got yourself a favourite: he could easily be retooled as a teacher in the high school setting.
Key Scene: Parker, seeking advice on his new arachnid predicament, approaches Connors in the school laboratory after hours, only to witness the horrifying transformation. The pair struggle to control their new powers in a lab-bound smackdown: expect more than just a few test tubes to get smashed…