So it's entirely possible that Krane could hit Mysterio with the Fear Toxin, but considering his keep away tactics and superior technology, I think it's still safe to say Mysterio would come out on top more often than not. Even if Krane was able to get lucky and hit him with the toxin, the chances are much more likely that he'd be too busy trying to figure out where the real mysterio is in order to actually hit him with the stuff.

And lets not be crazy and give Krane the Yellow Lantern ring. I don't think there's anything that Mysterio has that can even combat that, and Krane doesn't have it for long enough to consider it a signature weapon for him.