An idea to nerf Fizz, but not badly. A fair nerf.
Make it so the 2nd half of his Playful/Trickster makes him targetable.
Right now, I feel like there is a disconnect in the counterplay of the spell. Because he's supposed to use the first half of it defensively to dodge CC and damage, and the second half offensively to land the damage on you. But when he's untargetable for the offensive portion of the spell too, what can you do to him aside from just dashing or flashing out of the area of effect?
Being able to knock him backwards or to Zed ult on him to become untargetable to dodge his damage should be a viable counter-strat. Also, make the spell cancel when he gets stunned like Aatrox's dash so even if you can't dash away, you can still avoid the damage.
Fizz should be trying to dodge these things with the DEFENSIVE portion of the spell and not still be rewarded for playing poorly just because he's untargetable the whole time.
Additionally, we MUST match the hitbox to the particle effect. Right now, it's embarrassing to you as a company that the hitbox is that inaccurate.
I think Fizz would be more fun to play against, and require a bit more smarts to play as, if this change was implemented.