So I've seen a lot of people playing Viktor lately who have no idea what they're doing, building the wrong items, not landing their skill shots, and ulting at the wrong times. In this guide, I will explain how to fully utilize Viktor's true potential in the match.

I like to start out with the pros / cons so that people know what they're getting before dishing out 6300 IP or 975 RP

PROS:
Very strong early game
Out harasses almost any mid
Nice AOE crowd control in team fights
Insane AOE silence and massive damage ult
Good range for laser
Relatively low mana costs
Stop ganks easily
Different ways to play him (Augments)

CONS:
Falls apart if not fed or farmed
Extremely skill based
Hard to master
Only 5 item slots

I use these runes on almost all my ap carries. They help Viktor dominate his lane early and provide nice magic resistance for defense against the other mid.

This rune page provides-
+13 magic resistance (helps towards harass and in 1v1s against other mid)
+10 magic penetration (great for harass with Viktor's Q+E combo)
+15 ability power (good for early lane dominance and getting first blood)

I choose these masteries for a bunch of reasons. Maxing out the offense tree provides great damage early helping towards early game dominance of the lane. This will allow you to deny the enemy of farm and pushing them back towards their tower with your Q+E. Putting a point into Summoner's Wrath is great for the extra 5 AP when ignite is on cool down. Putting a point into Swiftness is also always good for Viktor so that you can land your Q and have your shield up before they have time to counter attack.

In my eyes, these items are absolutely perfect for Viktor. These items will allow you to have a good mana pool early to spam abilities, a decent ammount of health, and a nice bunch of ability power to crush your opponents. That is why I think rushing ROA is great on Viktor. The ROA gives him great balance. After that I pick up Sorcerer's Shoes for extra magic pen. and to pop off my Q more easily. Getting Rylais after that is a great buy because it allows you to tank some damage and stay in team fights for longer. It is also great because you can do massive damage while slowing the enemy, making it easier for you to chase for the final W+Q+E combo. After Rylai's I like to pickup Augment Death and rush into rabadon's deatchcap. Lastly, I like to pickup a Gaurdians Angel BUT the last item is completely situational. Some of the items I like to pickup are Gaurdians Angle, Quicksilver Sash, Archangel's Staff, Abyssal Scepter, or a Void Staff. And lastly, always remember to elixir it up.

Boots 3 health pots -> Sorcerer's Shoes
Doran's Ring (sell later)
Catalyst the Protector -> Rod of Ages
Giant's Belt -> Rylai's Crystal Scepter
Hexcore Augment Death
Rabadon's Deathcap
Situational item (most of the time I pick up a GA)
ELIXIR UP!

(Q) Power Transfer-
Maxing out Viktor's Q is extremely important. Having it maxed out by level 8 allows you to completely dominate the lane. It does insane amounts of damage while providing you a shield. It is a much better ability early than late because of the AP ratio scaling.

(W) Gravity Field-
Gravity Field is Viktor's AOE Slow & Stun. His W is very a very important part of Viktor but it shouldn't take much priority in the skill leveling sequence. Leveling up this ability only lowers the cooldown and increases the slow by small percentages. This ability is great to use in team fights. I like to use it to target the squishies or any carries. It allows Viktor to easily hit multiple people with his Death Ray. It is also a great ability in case you are ganked. Just throw the Gravity Field on the floor in front of you and run through it towards your tower. It makes ganking extremely hard for the enemy jungler. It is an awesome ability because it lets me play very aggressively in lane because I am almost gank proof.

(E) Death Ray-
Everyone knows Viktor for this ability. When Viktor casts his E, a laser shoots out of the arm extending from his back. It is a nice and cool visual effect and leaves an after burn on the floor. I like to use this ability more late game than early because of the AP ratio scaling and high mana costs. But, once I have my catalyst I am pretty free to spam my abilities. I like to cast Viktor's E when someone is running away or coming to counter attack from my Q. Using Viktor's Gravity Field can help line up a good Death Ray in team fights hitting multiple champs.

(R) Chaos Storm-
I put a point into his ult whenever I can just because of the sheer AOE damage + silence. You want to pop his ult in a team fight whenever it is landing on the most people. His ult does the most damage when first deployed, not after. The after damage isn't as useful as the initial burst. Below is a video demonstration of the power of Viktor's ult and a few other things happen. I will explain below.
Play Video
So I try to stay in and out of the team fight to make the most damage and fall back when my abilities are on cooldowns. My team initiates and then falls back but I know we can win if they run off of tower. So, our team falls back and they decide to run off of tower's range. This is where I made my move. I throw my gravity field down stunning Shyvanna and Ezreal so that I can land an easy Death Ray hitting 3 people in total. After the stun, I throw my ult down silencing anyone in it's range so that I'm not hurt and I deal massive damage to the other team.

Bringing Ignite and Flash is probably the most viable choice on playing Viktor. It is great for grabbing first blood and lets me get fed. Whenever I engage in a 1v1 I poop out my Q (good to cast first for the shield), then my W, E, and ult. Most of the time they are not entirely dead but will flash away. I like to flash towards them, pop a Q and an ignite. This is most of the time guaranteed first blood.

By the end of the day I think Viktor is an extremely underrated strong champ. Most of the people doubt Viktor's true potential because he is very skill based and takes a lot of time getting used to. He is a lot of fun to play and I highly recommend giving him a try.