First you need to know: Viktor is not an easy champion to play at first. You can find some users playing him without any kind of skill, and that's because of his difficulty and the low information about how to play it. Why is that? Because it's not a trendy champ, and pros don't usually (almost never) take him. However, that can turn into an advantage, because people don't know how to play against him.

Viktor has, as main position, middle lane. He can also be played at top lane, but I'd rather put there a more tanky champion. Moreover, if Viktor plays mid can help both lanes and he has the skills to do so.

His range and the power of his abilities can turn him into a lane bully, but his better face appears in late game. Never in the frontline (he has no abilities to escape), Viktor will try to CC the most enemies possible and throw his ulti in the middle of any teamfight.
Anyway, first is knowing his abs. Here we go.

Q: Power transfer

ACTIVE: Viktor sends a device at an enemy unit to blast them for magic damage. The device then returns to him granting a shield for up to 3 seconds. It has a reasonable mana cost and has a good shield, but this shield (usually) comes after the enemy you are facing has already hit you. That's why it won't help you some times to cover from enemy spells.

W: Gravity Field

ACTIVE: Viktor conjures a gravitational imprisonment device at a target location for 4 seconds, slowing all enemies that pass above it. Whilst under its effect, enemies generate stacks every 0.5 seconds; at 3 stacks the target will be stunned for 1.5 seconds. Hard to use against ranged enemies or fast ones, but very useful late game in teamfights. It has a good mana cost but it is kind of difficult to master.

E: Death Ray

ACTIVE: Viktor uses his robotic arm to fire a 500-unit length laser beam across the field in a chosen path, dealing magic damage to every enemy it hits. Without doubt, it is the most powerfull skill you will use. Don't abuse of it at start, to farm in lane, because its mana cost is so high. In middle and late game, Death Ray will be your way to finish enemies.

R: Chaos Storm

ACTIVE: Viktor conjures a chaos storm at the target location, dealing magic damage and silencing enemies in the area for 0.5 seconds. The storm cloud remains for 7 seconds afterwards, firing lightning bolts at every nearby enemy every second. While the storm is active Viktor can re-activate Chaos Storm to move it to the cursor's location, with the storm moving faster the closer it is to Viktor. Another hard skill to use that turns useful in teamfights. Because of its moving capacity, it can kill more than one enemy after a TF.


He starts with and object (Hex Core) that can be augmented with one of the following. Each one gives some benefits and improves one of Viktor's skills.

Power

The item now grants him +3 ability power per level, +220 health and +6 health regeneration per 5 seconds. Also, Power Transfer increases Viktor's movement speed by 30% for 3 seconds.

Death

The item now grants him +3 ability power per level and +45 ability power. Also, Death Ray sets fire to enemies, dealing 30% additional magic damage over 4 seconds. This is the one you should purchase. Is the one that makes Viktor a fearable champ that you don't want to meet in the battlefield.

Gravity

The item now grants him +3 ability power per level, +200 mana, +10% cooldown reduction and +5 mana regeneration per 5 seconds. Also, Gravity Field's cast range is increased by 30%.