Full Crit Fizz Build

General

1. You go Full Crit.
2. You go in and play around Hail of Blades to burst enemies.
3. You back away and wait for Hail of Blades. Repeat.
4. This build works best if enemy team has squishy champions. If you are against a lot off-tanks/bruisers, this might not be best build. You can make it work, however, by rushing Lord Dominik's Regards.

General

1. This build shines with 100% crit. You will instakill squishes. Until that, it might be challenging to 100-0 anyone. Look for opportunities to go in and score kills. Also focus on farming minions if possible (to scale faster).
2. Wait for your moment to go for a kill. You have a big burst thanks to Full Crit and Hail of Blades, but you are squishy. And outside of Hail of Blades procs (especially early game) you don't have much damage.
3. Snowball / Mark is an essential cooldown for this build. Do not waste it or even wait to hit the enemy at point-blank range to ensure hit (so you follow them, if they Flash).
4. Enemy team might not check your items right away, you could use that for your advantage to nuke unsuspected enemy.
5. After they checked your items and noticed that you have damage and are squishy, they are going to target you in fights. Be careful, after early game probably you need to modify your playstyle and stay back and wait for a good moment to join fights.
6. If they have tons of CC, get Mercury's Treads, Edge of Night or even Mercurial Scimitar to counter that.
7. If you are not doing well, or an enemy team is slightly ahead, you can adapt and buy tank items. Worst case scenario, you can sell everything late game and 'respec' into full tank.

Champion

1. Fizz E Flash Combo: Use Playful / Trickster (E) and when you are about to land, use Flash to the place you want. Do not use E second time!
2. Want to push turrets faster? Your Seastone Trident (W) resets auto, and it also bleeds turrets, so apply DoT to both turrets if possible.
3. You can use Chum the Waters (R) to disengage or to separate the enemy team. Somebody from the opposite team goes in? Just R into their team to disrupt the fight and slow them down.

Riot

1. Since Fizz can move through units, find opportunities in lane to walk through minions and apply Seastone Trident's passive - following it up with the ability's active attack after a few seconds.
2. Fizz's ultimate ability, Chum the Waters, can be aimed at an enemy or towards the area where you think they'll be going.
3. Fizz's spells scale off Ability Power - consider getting items like Zhonya's Hourglass or Banshee's Veil against teams that have high burst threat - and items like Lich Bane or Rabadon's Deathcap if you think you can survive without the Health.