First off, I'd like to say Viktor is a bit difficult to play early game. Phreak rightly says you can trade blows and mostly come out on top, but that doesn't mean you can just dominate the lane. Anybody with an attack that has higher range than yours can beat you down with no trouble, unless they can't dodge your death ray or don't utilize it correctly to keep you from getting the shield from power transfer. Mana is also a problem for him early game, so taking a mana potion instead of a second health potion can be very beneficial towards your poke ability, but only if you're sure you can avoid damage.

In my first build, I show a bit more early game way of playing, focusing on having lots of HP late game. This build suffers heavily from mana problems once you hit 18, so make sure your team will be able to spare you blue every time it's up.

In the second build it's all about mid-late game, using the extra scaling and mana on Archangels Staff to get in lots of damage in teamfights and sustain lots of poke outside of them. This build doesn't need blue at all, although it is helpful, and you should still try to pick it up when you can, making sure you don't take it from somebody in need of it. This build suffers from lower HP, so be sure you're not in a vulnerable position during fights. This is my preferred build.

On with the zapping.

For runes, I take flat everything. This is not always optimal, it's just the runes I have purchased, and I prefer the early game power for Viktor, as he scales well into mid game with his Hex Core.

9 Magic pen reds, for obvious reasons.

9 health yellows, for extra sustain against mid characters. Might want to consider switching for HP per level.

9 AP blues. Again, for obvious reasons, although you might want to consider switching these out for AP per level.

3 AP Quints. Non negotiable, in my opinion. Others may disagree, saying more magic pen, but I don't really think it's necessary. Up to you.

21/0/9

Self explanatory, really. Lots of Damage output, extra mana and mp5, longer buff duration. Standard mage build.

12/9/9

Bit of a strange one, this. Viktor only really has range of any note from his easily avoided Death Ray, meaning he needs to get close. This is counteracted slightly mid game by the amount of shield power transfer generates, but I needed a bit more. So I dove into the defensive tree, following Phreak in that regard. I took 3 points in Magic Resistance, as more than likely their mid is going to be an AP, putting a last point into armour for that rare occasion where it's an AD, then moving straight into the HP.

The rest needs no explanation, Simply the other mastery page without going deep into the offense tree.

Item builds are tricky on Viktor. He needs to spend more money than any other caster early game, because of his Hex Core. It does give really nice stats and is well worth the money, but I think he needs other things before taking it.

Open with a Sapphire crystal to make poke and farm easier, 2 health potions for sustain, or optionally, instead of a second health potion a mana potion.

From here, it's situation. If you're farming well, and not taking too much damage from harass, wait until you can afford to upgrade to Catalyst or Tear of the Goddess and get at least basic boots. If you've managed a kill even better.

ALWAYS get a Rod of Ages or Tear of the Goddess before even THINKING of augmenting your Hex Core. You need the rod maxed going into mid game, and the tear needs a big head start if you want it to be worth the money you spent.

Hex core choice is your own. I prefer Death, however Gravity gives great bonuses that sync well with an Archangels staff, and Power has an OK effect on top of making you more tanky.

Everything else is fairly straight forward, Rylais to make your ult useful besides the initial drop damage, Will for sustain, Deathcap for massive damage output.

Most of the time I will purchase my sorcerers shoes before augmenting, although basic boots should do if you're not afraid of being ganked.

Feel free to purchase other items, for example taking more AP instead of the sustain from will if you're not worried about being attacked yourself, void staff is a good idea.

Power transfer is your main output early game, so maxing it first is a good idea. Gravity field isn't really useful until level 6, if you need to drop a combo on somebody, so taking it later isn't a big loss, and the extra harass damage is extremely beneficial. Most ganks wont happen until level 4 anyway, so you're safe enough that you don't need it immediately.

There isn't really much leeway here, I think, so I wont bother listing alternatives. If they're absolutely terrible at dodging death ray, one could consider levelling it first, but it's not worth it 9 times out of 10.

Summoner spells are completely up to you. I like teleport as it gives me a farm and EXP advantage over other mids that didn't take it, and flash is usually a get out of jail free card.

Good Options:
Ghost
Ignite
Cleanse
Heal

Do not take:
Surge - Seems like it might be nice on paper, but it's really only good for surge damage champions, like Karthus or AP Shaco. I say surge damage because their main damage all goes out at once, through boxes or Requiem, and sometimes you need the boost. Viktor does not need the boost.
Promote - A support option, may be viable, but really not worth it.
Revive - It's revive. It's only good for lolz.
Clarity - You wont use it every time it comes off cooldown late game
Clairvoyance - For supports
Smite - Not jungling

Build 1:

Pros:
- Lots of HP
- Good Damage and control
- Sustain to level 18

Cons:
- Lower mana
- Damage not as high as it could be
- Still Squishy under lots of pressure

Build 2:

Pros:
- Lots of Mana
- High damage output, very good control
- Sustained through the game

Cons:
- Less Health
- Squishy
- Slightly difficult early game

Viktor is good at what he does. Don't try and change that, it wont end well. He's an AP nuke with good CC and very little defensive options besides using Gravity field and running like a little girl.

Mitigation through Power transfer borders on laughable, might save you in a few situations, but nothing you can do will change that.

On a final note, if anybody has any formatting advice, such as how to link items and such, I'd appreciate it. I know the guide isn't pretty, but it works for me.