Burst damage and backline assassination.
Burst damage and target access
Damaging a lot health champion inflicts adaptive damage and harvests a soul form the victim.
Gain a burst of Lethality and Magic Penetration after using a dash, leap, blink, teleport, or on leaving stealth.
Collect eyeballs for champion and ward takedowns. Gain permanent AD or AP, Adaptive for each eyeball plus bonus upon collection completion.
Unique champion takedowns grant permanent out of combat MS.
Empowered abilities and resource manipulation
Gain 10% CDR when you reach level 10. Excess CDR becomes AP or AD, Adaptive.
Gain increasing amounts of AD or AP, Adaptive over the course of the game.
+5 AD or 9 AP
+6 Armor or 8 MR (match-up)
Dark Harvest burst damage pattern synergizes well with your explosive dps nature, helping you one-shot most targets in drawn-out games.
Between Fizz's [Q] and [E] Fizz can easily proc Sudden Impact for bonus Magic Penetration when jumping onto his target.
Fizz is an assassin and is all about kills and snowballing and Eyeball Collection is the rune here that does just that.
The bonus Movement Speed from Relentless Hunter is excellent for empower your ability to roam and find picks in the jungle with your [R].
Hit that mid-game 30% CDR on fizz allows you to get multiple rotations of a well-timed [E] off to dodge important incoming damage.
Gathering Storm on Fizz puts you in position to assassinate anyone in the late-game with a single Magic Penetration item.