Increase the cool-down on Fizz's E
that's really all he needs to be balanced.
A 5 second cool-down on E is a bit much considering the power of the ability (a short zhonya's, reposition, aoe slowing nuke, that can negative EVERY ability in the game (except possibly ignite)).
Not to mention he WILL buy a zhonya's, effectively allowing him do 2 full rotations of his abilites (ok, only W once) while remaining invulnerable the entire time.
look at that cute face