Lore:

Centuries ago, an ancient water-dwelling race built a hidden city beneath a mountain in the sea. Though these creatures had their enemies, the city was an impenetrable fortress, and, in the safety it provided, they grew complacent. Fizz, however, harbored a curious spirit that could not be satisfied living so cushioned a life. Unable to resist the allure of danger, Fizz had a habit of sneaking out of the city to look for trouble. In his many adventures he grew to be a powerful fighter with a sharp cleverness that let him skirt danger with ease. One day Fizz returned to find the city abandoned: his people had vanished, leaving Fizz without a clue to explain their disappearance. With nothing left in the city to keep him, Fizz salvaged an enchanted seastone trident from the ruins and set out alone.

Fizz wandered the ocean in search of his people for years, using the skills he’d learned during his adventures as young boy to survive. Finally, Fizz discovered the port of Bilgewater. He was fascinated with the existence of life above the water and could not resist exploring the island. In his endless curiosity, Fizz inadvertently meddled in the affairs of the humans who lived there, and his presence did not go unnoticed. His mischief angered many residents who eventually sought to capture or kill him. Fizz found himself cornered, and he prepared to return to the sea despite the fondness he’d come to hold for Bilgewater. As he stood at the docks, a massive dragon-shark attacked the port. Fizz defeated the beast, using his resourcefulness and knowledge of the creature’s weaknesses to his advantage. Having earned the gratitude and respect of the humans, Fizz decided to stay in Bilgewater. To further serve his new home, he joined the League of Legends.

“Fizz makes even the saltiest sailors of Bilgewater look like drunken landlubbers in a fight. Good thing he’s on our side.” – Miss Fortune, the Bounty Hunter

Hi, I'm JohnGonca, I've played Fizz since the day he came out, and I can tell you, that it's by far my favourite champion.
In this guide I'm gonna show you both builds I use both for Mid and Jungle, and giving you all the tips I know about this little fellow.
I can't grant it's the best builds, but by experience I can say they are pretty good.
So yeah I hope you like the guide and enjoy playing with fizz as much as I do :)

Classic:

Atlantean Fizz:

Trunda Fizz:

Fisherman Fizz:

Abilities:

• Urchin Strike [Q]: ◦Fizz dashes through his target, dealing normal attack damage plus additional magic damage.
  
• Seastone Trident [W]: ◦Passive: Fizz's attacks rend his target, applying a damage over time effect that strengthens if the opponent is low on life.
  ◦Active: Fizz's attacks are empowered, dealing additional magic damage and causing grevious wounds to his opponents.
  
• Playful / Trickster [E]: ◦Fizz hops onto his staff, becoming untargetable. He may then choose to slam the ground or hop off to another location
  
• Chum the Waters (Ultimate): ◦Fizz flings a fish that can bind itself onto enemy champions - After a brief delay, a Shark will emerge from the earth to eat the fish, dealing damage and knocking back all enemy champions.
  
• Nimble Fighter (Passive): ◦ Fizz's dexterity allows him to ignore unit collisions and take less damage from basic attacks.

Items:

This items are designed for a great outut of damage trought out the whole game, until completing Rod of Ages you can complain about lack of Ap, but you soon forget it after buying Rabadon's Deathcap.
This items will provide great health wich will result in and awesome, tons of damage dealing, Off-Tank.

For the last item, for me, there are three great items you can choose.
You can buy Lich Bane, my favourite, gives you movement speed, increasing to about 400, gives you ability power and a great passive, wich deals tons of damage.

You can also buy Nashor's Tooth, wich gives you AP, Cooldown Reduction by 25%, and atack speed.

In the last case if ur thinking of really maxing your AP you can finish off with a second Rabadon's Deathcap, which provides massive AP, notice that the passive of Rabadon's doenst stack, only the passive of the first Rabbadon's will be used.

Ghost:

Provides awesome escape mechanism.

Ignite:

Provides great finish for when you can't finish an opponent or just to ensure the kill.

Pros:

• Great Power throught out the game.
• Huge amount of life without loosing much power.
• Great mobility.
• Great escape mechanism.
• Good cooldown reduction.
• No worrys about mana (Except early game, a little bit of strugle if u use too many skills to farm)
• Awesome damage output the entire game.

Cons:

• A little bit squishy early game.
• Not try to kill until reach lvl 3, but keep harassing until reaching it.

Jungling:

Fizz is a very powerfull jungler, you can start by killing Blue, then the wolves, followed by wraths, Red and if you have enough life, kill the wolves again.
At this point you're at lvl 3, which grant you Playful / Trickster [E] wich is fundamental for ganking.
Look at the mini-map and look for ganks, if you dont have any, carry on jungling, at this point if u have vampiric specter you dont need health potions for the jungle itself but u might need it for ganking.
You can return to the jungle by killing the wolves, wraths and then the golems, look for ganks again.
At this point there is not much I can say. Start the gank by pinging the oppenent you're ganking, start by hitting with the combo of Seastone Trident [W] and Urchin Strike [Q], and than land the Playful / Trickster [E] for the slow, use Chum the Waters [R] if you think he can get away or just to ensure the kill.

Farming:

When farming try to cut on the use of your skills, unless you have blue buff, in this case use Urchin Strike [Q] and Seastone Trident [W] all the time to grant last hits, but save Playful / Trickster [E] for possible ganks you might receive.

So yeah, that concludes my guide, I hope you like it.
Rate and give me your oppinion in the comments, Thank You Guys!
(I'm thinking of adding my dominion build, if u want it, tell me in the commenst otherwise, I probably wont release it, has I dont see many people playing dominions)
Cya In-Game Guys ;)

Some Scores:

I did the guide all by myself, but I want to give a special thanks to JhoiJhoi, her guide help me out quite a bit on making my guide looking better, etc.
You can check out her awesome guide right here:
JhoiJhoi's awesome guide about guides