Hello im from Turkey I'm playing in TR server. İm a viktor fan he is one of my three champions.
I played over 3 months with Viktor. And i created this build for viktor fans as well.

First of all Viktor is not Combat initiater. Do not try to start team fights. Just harrash from safe distance. Until team fight starts.

You are the 2nd or 3rd man in team fights and Viktor is Zonner Laner. With nice Crowd Control skills So dont try to go in 1v1 until you are experienced with viktor. You will loose it.

Viktor's purpose is to harrash enemy and tackle them in team fights with Gravity Field nice slow stun Arcane Storm nice damage with AoE. and enemy homing for last hits if neccesary. And AoE Silence ability. "0.5 sec." Definitly you will shock enemy with W R E Q combos.
very important point. instead of burst viktors. This viktor has more HP more sustainable damage so be sure you can get in and out from combats.

and thanks for reading my guide. its my first one. Read it Vote it.

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Early big ap makes viktor counter enemies much more easliy also getting early kills gives huge advantages on gettings item.

mana regeneration should be max efficiency. also You can switch Greater Seal of Scaling Mana Regeneration them with Greater Seal of Mana Regeneration and You can directly go for Augment: Death

magic penetration there is no better rune to use with Viktor in this section go for it.

Starting items Having some more Speed always good and helps run out of enemy combos bursts. Health potions and Mana potion for more harrash and more fun.

Mid Game İtems
Chalice of Harmony Mana regeneration and resistance for magic attacks probably u will counter with enemy AP carry in mid, and u will gain nice mana regen. So u will keep harrasing enemy.
Augment: Death definitly best addon attachment for Viktor More AP more harrash. Also strong lanning capability cause of burning condition makes %40 more damage on enemy over 4 sec.
Athene's Unholy Grail Core of our spam build. Cooldown reduction(cdr) more mana more magic resistance.
Ionian Boots of Lucidity More speed More CDR.

With this you will have 3.05 sec on Power Transfer 5.89 sec in Hextech Ray
6.68 on Gravity Field optimal 200+ AP so you are now big threath for enemy AP carries. also in ganks you can use your zonning abilities much more often. As i said this is spammer build. You will spam em alot.
Late Game or if you get 2-4 kill in early/mid game period or you farmed well with your Augment: Death

Lich Bane Definitly Best used with Viktor's Power Transfer because of you can hit enemy non-delayed with normal attack after cast Power Transfer im talking about 1k+ damage every 5 sec. 3.05 sec Power Transfer cdr, +2 sec Lich Bane cdr
Rod of Ages more health point more ap more mana
VİEW OF COMPLATED CORE.
last two slot you can get items for situational if there is 2 tank or tanky enemies you can get Rabadon's Deathcap
if there is hardcounter for viktor you can get Zhonya's Hourglass because of 2.5 sec invulnerability saves you multiple enemy burst damage.