I am writing this guide for you to get out of bronze, this does not apply to silver and above. Fizz is an amazing champion to play at lower ELO due to his enormous damage output and fantastic escapes and so this build is for high-risk, high-reward play style. I've noticed this works amazingly in Bronze since most players don't know how to effectively counter an aggressive Fizz in lane. This entire guide is based off playing an aggressive lane Fizz and a guerilla mid game Fizz. The build is all about killing carries in 2+ vs 1 situations and walking away while laughing. Enjoy

In my experience starting a flask and 3 pots on Fizz is the best way to go for almost every matchup. The lane sustain it gives you is amazing and if you should make a mistake early on, it makes the aftermath much more forgiving. Always try to wait until 1200 gold to buy Sheen as a whole. Normally this should take you until around level 5 providing you haven't killed mid yet in which case you should be able to get sheen and boots. Your second back should at least be BW if not a full LB. If the game gets past 35-40 mins, build a GA. Otherwise only get it if your being focused early.

In bronze, no matter the matchup, start "W". This skill is going to get you most of your early kills and almost all of your CS. Remember it does the most damage against targets with low HP and the DOT it applies makes healing much less effective. You should almost always take "Q" second so you can W-Q harass but if your getting zoned out (by Kayle perhaps), take "E" second so you can escape a life threatening situation. Once you hit level 3 you can combo down and kill almost any pushed enemy with ignite. Max "E" first to lower the CD and try to only use it for escapes or confirmed 1-2 vs 1's. Once you get Zhonas I find it very effective to initiate a teamfight with your ult against a group, "E" in on top of them and blow hourglass immediately, when you regain control "Q" through the champion closest to your team and run. Not only will you deal a massive amount of damage to multiple enemies, you will also slow them and cause them to try to attack your untargetable body leaving your team tons of opportunity to destroy them. Always try to use your ult when you are as close as possible to the target, missing it will often lead to the entire enemy team turning around and focusing you.

Pros

+Many escapes
+Very hard snowball
+Advantage over most mid champions
+Can easily recover from early deaths
+Strong roaming ganks
+Amazing early-mid game

Cons
-Squishy as hell
-Mana hungry at early game
-Easy to beat with teamwork
-Skillshot ult
-Falls off somewhat late game

This is by far the most important part of this guide. When I say your going to carry the game, I don't mean your going to do it by being 25/0. Your going to do it by helping bot or top lane and then being 25/0. You are mid, you are in the best position to help your team be it bot or top. If your winning your lane, make them win their lanes. The quicker towers go down the quicker you can start picking apart their carries in teamfights and win your team the game. The second you drop your first tower, roam. Hunt down every squishy they have and then jump away laughing.

Fizz has to play a little differently with every matchup so I'm not going to go over all of them since most can be won just by playing correctly. I'm just going to give the matchups to absolutely avoid whenever possible.

Diana
She bursts just as well as you pre 6 and she can out sustain you with her shield. Post 6 your damage output becomes greater but she can still out sustain you 1v1. Nightmare when fed.

Mordekaiser
You cant get anywhere near him without taking "Q"s to the face and when you do reach him his passive and "W" make him hard to burst. Without jungle help or kills from roaming he'll be a problem for you the entire game.

Kayle
If she takes "E" first you cant get anywhere near minions without getting beat up. She has a heal for sustain and speed, a heavy damage slow and, of course, invulnerability to counter your burst and ult.

Zed
This is more of a tossup in my opinion when it comes to bronze players. He certainly is a counter to you in many ways, but many bronze Zed players are just terrible. If you can get the advantage early game by dodging his blades and always have "E" ready to dodge his ult, you can pick him apart. Just make sure you don't give him opportunities to gank other lanes.

Lissandra
This is just a terrible matchup. You'll either burn all your mana trying to farm or fall behind while being zoned. Luckily, very few people play Lissandra and even fewer play her well/

Akali
Just let her push and on your second back buy a stealth ward to see through her "W". Post 6 always be prepared to dodge her "Q" and burst quickly.

Ryze
No one in bronze plays Ryze well enough for this counter to matter.