Fizz is a champion that gives enemy carries nightmares for weeks. Some say he falls off late game, but the only thing he falls off of late game is his trident as he lands on top of your adc taking out 3/4 of their health. If you are fighting against a Fizz, weep in sorrow and cry as your loved ones die around you. If one of your allies has a Fizz ult on them, leave them as a sacrifice to the mighty fish demon and pray that you go unnoticed. With this guide, I will not teach how to defend from the monster as there is no reason to go against your inevitable demise. This guide only teaches the road to inflicting death and destruction.
Did you know Fizz's actual title is "The Terror of the Void." Unfortunately, Rito Game accidentally put his fish skin as the basic and the Void Fizz skin as an unlock. Then, in true Rito Game fashion, they refused to acknowledge the mixup and created a new champion, Cho' Gath, to be the fake terror of the void.
TL;DR: The vast majority of Fizz's power is locked behind a paywall. Until you have the Void Fizz skin, don't play Fizz.
How to Play the Early Game
First and foremost, back off. You are not yet an elder god. Give up cs, towers, lane pressure. It will all be worth it later when they give up their firstborn (aka: their adc).
For a starting item, build either corruption potion (if you want to increase the evil in your soul) or doran's ring (if you think you are already corrupt enough). Just farm up early, only taking trades if the enemy laner is acting stupid.
Most novice Fizz players seem to think that Fizz needs to rush damage. This is just plain factually inaccurate, as the demon lord Fizz's base damages are actually incredible. The issue the demon lord has is that at the beginning of the game he is still a mortal and not yet the Lovecraftian horror he becomes at 30 minutes. Thus, in the vast majority of games rush a defensive item into your lane matchup. Getting an abyssal or zhonyas early will allow you to outtrade your laner and survive until you can kill them in one combo. Picking up a defensive item, such as negatron cloak or seeker's armguard, and then a sheen is a very effective item combination to kill your opponents in the midgame.
How to Play Fizz After 10 Minutes
Laugh at their corpse, unless it is a yordle. Then their wont be a corpse after your pet monstrosity devours what little meat they have to offer. I recommend not wasting your ult on yordles, they are too small to be an efficient sacrifice.
You lose them all. Just survive and kill them at level 6. Except Vayne mid. Murder Vayne brutally at all stages of the game. Care of Bard top getting ahead Kappa.