Hi I'm snowyfreezer this is my Fizz guide. I'm not an expert player and I am not the best Fizz player so Feedback would be appeciated.

What is fizz?
Fizz is a assassin that can do back flips. He can easily kill someone if he lands an ability. His kit isn't complicated and is simple once you know what his abilities do.

Pros

+ Is a Fish + Has an ability to do backflips and go untargetable + Excellent burst + Good escape (depends on your position) + Depending on what you like fun

Fizz overall is an assassin that excels in killing people while being slippery.

Cons

- Is an Assassin and Assassins Fall off late - Susceptible to CC like everyone - Melee Champ - Hard early Laning Phase - Sometimes not easy to hit Chum the Waters depending on opponent - You have to auto attack many times

That said Fizz is not overpowered in anyway. His early laning phase can be hard to manage if you get an opponent that knows how to poke you down before level 3.

Domination

Electrocute Electrocute: Pretty straight forward. A damage rune that will help you in trades or killing someone. The other options wouldn't really help you in lane. Sudden Impact Sudden Impact: The Magic Penetration overall increases your damage as it is every easy to proc with a dash. Zombie Ward Zombie Ward: After the rune changes this rune is much harder to use as it no longer extends the duration of your own wards.This can still be viable if you buy Oracle Lens. Relentless Hunter Relentless Hunter: Out of combat movement speed which is very useful when roaming or moving around the map in general. Ravenous Hunter Ravenous Hunter: The spellvamp you get from this rune can help you in close fights from using your abilities. Ingenious Hunter Ingenious Hunter: Reduces the cooldown of your item actives so you may use them more often such as Zhonya's Hourglass. Ultimate Hunter Ultimate Hunter: Reduces the cooldown of your ultimate ability which gives you more chances to use it. Sorcery Celerity Celerity: with the recent changes basically useless since you don't have a movement speed boost. Scorch Scorch: This is an early game rune that does some burn damage that may secure you some kills. Nimbus cloak Nimbus Cloak: This actually doesn't feel too bad. After ulting you gain a burst of movement speed that may help you chase someone or run away.

Inspiration

Time Warp Tonic

Time Warp Tonic: Uses half of your potions Corrupting Potion which will help your sustain in lane and gives small amount of movement speed.

Biscuit Delivery

Biscuit Delivery: Gives you more sustain in lane as your are prone to getting poked.

Flash
Almost every champ takes flash. Very useful for escaping and gapclosing. Without flash you could miss out on kills or even escapes.

Ignite
Take this for early game cheese or finish off low health targets. Useful in order to start a snowball and reducing healing.

Teleport
Useful in hard match ups where you can teleport back to lane or help your laners by teleport ganking. Usually the safe option

Nimble Fighter Fizz is Ghosted and takes reduced auto attack damage There isn't a lot to this passive other than its ghost ability. Sometimes it will help you win auto attack trades and helps with CSing without getting creep blocked

Urchin Strike Point and click that dashes through the selected target. This skill is a simple targeted dash used to gap close or on a minion to escape or other things. You can actually go through walls if you are able to click a target on the other side of the wall. This ability also applies on-hit effects which is useful when you buy a Lich Bane.
Seastone Trident Passively basic attacks bleed your target. On activation the next basic attack does increased damage, if it doesn't kill empower your basic attacks for 5 seconds. There isn't much to this ability other than it being used for damage and is an AA reset.This ability can also help you CS in the laning phase where it gets a mana refund and cooldown reset on kill.
Playful / Trickster Hop on your trident becoming untargetable for the duration This is the ability which makes people hate Fizz. Using this ability you can dodge any skillshot other than tethers such as Fiddlesticks' Bountiful Harvest. Knowing when to use Playful / Trickster depends on if you know what the other champ is able to do.
Chum The Waters Throw a fish at the target location applying Seastone Trident and dealing damage after 1.5 seconds. Using this ability will deal a significant amount of damage. The damage this ability scales on distance which means close range this ability does less damage. Other than that this ability is pretty straight forward.

Starting Items

Corrupting Potion We want this item for the sustain it provides as usually in mid lane you'll be facing a ranged champion who can poke you down very easily. Generally a safe starting item. Recommended start.

The Dark Seal A pretty cost efficent item that increases the effectiveness of potions. You can buy this after your first back if you brought corrupting potion

Doran's Ring A doran item that provides mana regen and some health. Not recommended to start with. Can buy on first back.

Core Items

Hextech Protobelt-01 We want this item as it gives you a dash that can be used to finish off opponents or popping Banshee's Veil. Since Fizz has poor waveclear this item will help you clear the wave without using Playful / Trickster.

Lich Bane A Sheen item that will increase your damage as you auto attack. Overall increases your damage in a combo.

Zhonya's Hourglass An active that puts you in stasis allowing you to wait for cooldowns or dodge abilities. Also Provides some armor in case you're in an AD matchup.

Rabadon's Deathcap The wizard top hat will boost your ability power significantly, Allowing you to do more damage.

Void Staff The pointy stabby wand will penetrate 40% of an opponent's magic resistance. Almost required every game as at least someone will have magic resistance.

Situational Items

Morellonomicon The book will apply Grevious wounds on magic damage great for reducing healing.

Banshee's Veil The spell shield that will block a hit for you in case you need it.

Boots

Sorcerer's Shoes The standard shoe for if you want to do more damage with the magic penatration.

Ninja Tabi The shoe that gives you armor and reduces basic attack damage. Take this if you need armor

Mercury's Treads Boots that give MR and tenacity. Take this if you need magic resist or reduce the time of CC.

This is the hardest part about Fizz as

1. You're a melee champ

2. You don't have all your abilities lvl 1-2

3. No ranged waveclear

What you should do is try to get as much CS as you can early and don't take unnecessary poke.
Once you get level 6 assuming you didn't feed you can kill most laners with Chum the Waters.

Assuming you killed your laner you can freely cs while they're dead and push the wave so the enemy laner loses CS.

Trading in lane?
Usually you want to Urchin Strike in and AA and activate Seastone Trident auto attacking many times,using Playful / Trickster when you have to.
You don't have to do this exact same thing every time but you either use Urchin Strike on a minion to escape or Playful / Trickster
basically try and use one of your mobility abilities to escape
If your opponent is melee you can auto them to try and proc your W and start autoing them a few times

Roaming
If there's nothing to do midlane you can either back or roam bot side or top side.
You shouldn't force a gank just like how a jungler shouldn't force a gank unless a perfect opportunity rises.
If you actually do roam depending on the champion you may get your laners ahead and maybe a tower.

Kill combo?
Generally to kill someone you have to land Chum the Waters on them first. Other than that you have to proc Seastone Trident as it does a lot of damage.
When procing Seastone Trident you either activate it during the middle of the Urchin Strike animation so the first hit gets proced and continue autoing or you can use Seastone Trident as an autoattack reset.

Out Of Laning Phase
Alright so you made it out of laning phase and everybody is starting to group. What you want to do if you're ahead is to kill them very easily and proceed to take the nexus. Whatever you do make sure it is going towards the goal of destroying the enemy nexus not getting as much kills as possible. Since Fizz as an assassin falls off in the late game you are going to want to end the game early
Whatever you do, DO NOT DIE FOR NO REASON
Dying will give your enemies gold in turn will give them a chance to come back.

TeamfightingAs Fizz it is possible to flank the back line and land a shark making it easier for your team to win the team fight. Generally you are going to want for certain abilities to be used before you want to go in. You usually want to kill the easiest target depending on the situation.
Without Chum the Waters its going to be hard to walk up and use your abilites as if you engage with Playful / Trickster you're gonna be blown up.

Splitpushing
Well you may or may not need to splitpush you generally need teleport in order to splitpush,
usually when splitpushing you draw pressure away from your team allowing them to presssure baron or dragon while you go get a tower. Fizz can take towers decently using Lich Bane.Fizz is able to decently escape if somebody comes depending on the enemy champion

Late gameIf you didn't end the game early you're gonna have a bad time.
Generally the enemy will have defensive items that will prevent you from killing them, supports that can stop you, and adcs start to do damage.
Usually you won't reach late game as you should go for objectives and end the game.

All in all Fizz is an Ap assassin that has high damage with his abilities.

That is all for my guide, I'm not the best Fizz player by any means so feel free to share your thoughts.