About Fizz
Alright I have a bone to pick with this guy, but before I do, I'll acknowledge his weaknesses. He sucks until level 4, his ult can be dodged, and he falls over if cc'd while his E is on CD.
First, his combo seems too readily available to him. I'm talking specifically about his E cooldown. Other assassins/bursty champs like Ahri, (ult/charm) Yasuo, (windwall) and Akali (Shroud) have important abilities with cooldowns that prevent then from being constantly in the middle of a fight.
With fizz, I feel like there are a lot of cases that he gets away with too much. His E is essentially a free period of invincibility, and when you need to stop him from rampaging all over your team it's dumb that it's off CD as frequently as it is.
The other thing I'll mention about Playful/Trickster is that it should not delete targeted abilities or projectiles from non player sources. For example, stuff like TF's Gold Card and tower missiles shouldn't magically disappear when Fizz props himself up on a trident. This mechanic creates situations where Fizz will win, no matter what.
Besides this, I have no problems with him as a champion. I'm not calling for him to be gutted, I only want his E to be looked at a little.