What If Trevor Slattery had gotten his hands on Mysterio's equipment? I doubt he'd do anything bad with it but I'm sure he'd have some creative ideas in store given his acting skills alongside the powerful illusions (Sort of like comic Mysterio).
Not gonna lie, but Ben Kingsley would actually make a pretty solid Mysterio. And oddly enough, Trevor Slattery's character does fit with Mysterio being a failed actor in the comics. That's actually a very interesting comparison.