Pros
+Very Mobile
+Extremely strong all in potential at 6
+Powerful Mid Game
+King of Snowballing
+Troll Pole OP
Cons
-Squishy
-Ult is a skillshot, and can be dodged]
-Horrible laning phase
-Q And E can be flashed
-Melee

You want Morellenomicon as a first item because its cheap and you wanna hit 40% CDR at the end, Lich Bane is great since you do a lot of damage with it and work well with it, Zhonyas since your squishy, Rabadons for AP, void magic pen, and at the end you can sell you boots for Ludens Echo since it gives 10% movement speed which fills up the movement speed part and a lot of extra AP but no more 40% CDR.

Just rush Athenes and Abyssals, and skip You want Morellenomicon since Athenes gives 20% CDR. And no void staff since Zhonyas too good, unless they have no ad, like a APC.

Just go first item Zhonyas against Zed or etc.

Sometimes you wanna start Q vs SS champs like Ahri, etc, but most of the times you start W for easy cs and out trading at level one.

Butcher is good since Fizz can't cs very easily unless you use W all the time, but that uses too much mana. Assassin too good 2% increase, this is preference if you have mana problems take Meditation but Merciless is very powerful. Supports take bandit, dangerous game save you from ignite. CDR good but you can take other one, its preference. Thunderlords, not brainer, does too much damage. And for the ferocity tree attack speed is worse than spell damage, feast too good, and this preference I like the AD and the AP since Fizz auto attacks a lot. The last one is preference again, its about play style, if you use the slow E then you might take Oppressor, but I get fed too much so i take Bounty Hunter.

Greater Quintessence of AP: Fizz is an AP champion and needs AP for damage
AP runes: Same thing, needs AP
Heath Runes: Hp op, helps you survive in the early game if your facing hard match up, and theres really nothing better
Magic pen= More Damage.