Hey guys, I'm Purplosion and this is my first guide. Obviously this guide is about Viktor The Machine Harold. The reason I'm writing this is because every time I pick Viktor as AP carry in ranked games my team screams at me that he's terrible. I don't know why people say this, personally I think he's a great champion and I haven't done bad with him in any ranked games YET. Anyways, feel free to give me some feedback or ideas. Here are some Pros and Cons.
Pros

Amazing damage with any of the four builds.
Awesome at kiting
More than one way to build (keeps things interesting)
Good CC (AOE stun/slow and AOE silence)
awesome at creeping.
Decent range.
A lot of AOE abilities.
Free item.
Sleeper OP
Super awesome bugs like the Invisi-Laser.
Good at getting out of sticky situations. Just drop a Gravity Field, Power Transfer the nearest thing and run like Hell.
A voice rivaled only by Nasus.

Cons

People don't understand that he's actually good and think he's underpowered.
Moderately difficult to learn.
Double Ulti Bug was patched
Susceptible to CC.
Forced Item (some people see this as a Con, I personally like it)

To me, masteries are all up to personal preference. I run 9/0/21 because with that I get 10% cdr, longer buff duration, increased EXP (Getting to level 6 before your opponent is a VERY big advantage.), more movement speed, reduced time dead, more mana regen and mana, flash more often, and last but certainly not least 15% cdr on summoner spells. But if you feel another combination of masteries is more beneficial, go for it.

Runes- Not much to say about these, basically just generic AP mid runes. Other options would be MR glyphs/seals because you'll most likely be against an AP champ in mid, health regen seals, and I actually go with flat AP glyphs but for some reason that wasn't an option.

I used to hate flash, always thought it was unfair and just plain annoying. And then I started to actually use it and realized how great it is. Viktor doesn't have the greatest range so I would say flash is a must have to secure kills, get away, and flash-ambush unsuspecting enemies.

Ignite is also great to have on anyone. Gives you that little bit of damage you need to secure the kill early game. Also works amazingly on those mages with sustain like Swain, Ahri, Ryze, Vlad, etc.

Other viable options are Ghost for when you don't like Flash, Exhaust for that rare occasion that you get an AD carry in mid, Teleport if you think you need it, and I guess Heal if you actually use Heal.

Absolutely Not- Smite, Revive, Clarity, Promote, and Surge.

NOTE: I will not be repeating why I grab an item for each build. If an item is in more than one build I will only explain why in one build.

First up again is the Augment: Gravity Build.
I start out with boots three pots, the mana pot is optional if you find you're running out of mana early on but I usually take three health pots. Boots three pots is a great way to start on pretty much everyone. It gives you mobility to dodge skillshots, chase, and run away and allows for mistakes because you can heal it up with the health pots.

Why Sorcerer Shoes? Simply put, you don't need any extra cooldown reduction. You get 25% just from masteries and Augment:Gravity, add the 20% from the Blue Buff your jungler should be providing and you'll cap out at 40%. Only replace this item with Merc Treads if the enemy team has a lot of CC or if you're having trouble with their AP. Also if you want the full CDR with the Augment:Power and Death builds you can replace it with Boots of Lucidity.

Why Augment:Gravity? Augment:gravity in my opinion is the best Augment. You get 200 mana, some mana regen, 54 ability power at lvl 18, 10% cdr, and INCREASED RANGE ON YOUR GRAVITY FIELD all for 1k gold. What's not to love about this item?

Next up is Rabadon's Deathcap. The reason we rush this is because your previous items don't give any AP (Besides the 3 per level that your hextech core gives.) Rushing Rabadons is something I only do on this build. This is pretty much a must have on all 4 builds, don't replace it with anything.

Rylai's Crystal Scepter- An amazing item. Gives you health, ability power, and a slow with all of your abilities. This is a must have on all builds. Do not replace it with anything.

Will of the Ancients- I actually get this item last. I build the Hextech Revolver before getting Zhonya's Hourglass but I don't finish it until after. We get this item because it gives good AP and spellvamp. This item CAN be replaced but I only recommend doing it if someone on your team already has one.

Zhonya's Hourglass- This item is amazing if you can remember to use the active. Two seconds of invulnerability is priceless in a team fight. I realize you can't do anything while it's activated BUT it gives you time for your cooldowns to refresh and the enemy team often drops focus on you completely even after the effect is gone. The stats on it are also good. This item can be replaced and definitely should not be used if you often forget to use item actives.

Next up is the Augment:Power Build.

Why Catalyst the Protector and Rod Of Ages? Catalyst gives great mana and health sustain with it's unique passive. It also makes you a bit less squishy and gives you all the mana you need. I don't recommend replacing ROA with anything.

Why Augment:Power? Augment:Power is great for beginners. It gives you extra health and health regen and increases your movement speed for the duration of the shield that using Power Transfer gives you. It's great for chasing, running away, and avoiding skillshots while harassing.

Next is the Augment:Death Build.

Why build Augment:Death? The only reason to build this is that it gives great stats and makes you do more damage for a cheap price. While the damage is significantly better, I feel that Viktor does enough damage and would rather Augment Gravity or Power over Death.

Finally there's the build I currently use.

Why Deathfire Grasp? Deathfire Grasp is my favorite item. I build it on pretty much every AP carry that I play. It gives good ability power, CDR, an amazing active, and while you have the Kage's Lucky Pick you get increased gold per 10 seconds. Lead in with the item active then use your Gravity Field and Chaos Storm, making sure the storm follows who you want it to, then just Death Ray and Power Transfer for the kill. Very quick, very effective.

Do NOT blindly follow these builds. There are different situations where you might want to switch out a few items and that's fine. Here are some good item choices that you can switch out for.

Void Staff- If the enemy team is stacking Magic Resist it might be a good idea to buy these. BUT if you get it sell your Sorcerer Shoes for Boots of Lucidity or Merc Treads. I don't remember where I saw it but someone figured out that since the flat spell pen is factored in before the percent pen which means you do the same amount of damage with 20 spell pen and the voidstaff than you would without the 20 spell pen.

Abyssal Scepter- If the enemy team has an AP champ that's kicking your *** this is a great item to get. It also reduces the enemy's magic resist. It's a bad idea to get this and a Voidstaff.

Lich Bane- This is a pretty fun item. Gives you good ability power, more movement speed and magic resist and a passive that makes your autoattacks do damage equal to your ability power every time you use an ability.

Mejai's Soulstealer- If you're absolutely confident that you won't die a lot this is a great item. But if you buy it you will get focused in fights and ganked a lot. Make sure you can handle it.

Guardian's Angel- It's like a second life.

Banshee's Veil- Just to make sure that pesky Karthus doesn't get a lucky kill on you.

Anything else you can think of- use your imagination! Get creative and have fun with it.

First up is the Augment: Gravity Build. This one is my personal favorite just because I absolutely LOVE the range increase on Gravity Field.

Pros of this build-
Great Damage early on and late.
Increased Range on your CC lets you stay back a bit more in team fights to avoid getting focused.
Max CDR with Blue buff.
No mana problems.

Cons of this build-
SUPER SQUISH. This is the main problem I have with using this build.
If you use this build and then go back to using a different Augment it's very difficult to get used to the shortened range.
Your team might rage and call you a noob for not augmenting Death. This is only because they are stupid and don't know what they're talking about.

Overall Difficulty of this build - Out of my four builds I'd say this is the second hardest to use. It's never easy being squishy and you need to do everything you can to avoid being focused.

Next build is the Augment: Power. This is the one I started out with.

Pros of this build-
Tankiest of the 4.
Easiest to use.
Very easy to chase and get away due to the Power Transfer Augment.
Good Damage all game.
No mana problems.
Great sustain with early Catalyst The Protector.

Cons of this build-
Least damage of the 4.
Can't max CDR even with Blue Buff.

Overall difficulty of this Build - This is the easiest build of the four. I started out using this build. It gives the most health, there's no item actives to worry about, and doesn't punish mistakes as much as the other builds because you can just throw down a Gravity Field and use the movement speed buff on Power Transfer to run away.

Next is the Augment: Death build. This is the typical Viktor build that everyone freaks out if you don't use. I very rarely use this build and don't recommend it.

Pros of this build-
The most damage out of my 4 builds.
Great Early sustain with Catalyst The Protector.
No mana problems.
Good damage all game.
No one rages at you. WOOOOOOO

Cons of this build-
Zero extra utility from your passive. You got a bit more damage on a champ that has great damage already, congratulations.
Can't max CDR with this build even with Blue Buff.

Overall Difficulty of this build - This build is the second easiest of the 4. Very simple, but not as easy as Augment: Power build. Though I do not recommend it.

Lastly is the build I currently use. After testing many different builds I find this one to be the best.

Pros of this build-
Great damage all game.
Max CDR with Blue Buff, 35% without Blue Buff.
Good at chunking tanks with DFG.
Increased Range with Gravity Field.
No mana problems.
Increased gold with Kage's Lucky Pick.

Cons of this build-
Squishy.

Overall Difficulty of this build- I would say this is the hardest of my 4 builds to use. It has all the difficulty of the first Augment: Gravity build except it doesn't have WoTa and has two item actives to use.

So those are the pros, cons, and difficulties of each build. Picking which one is a personal preference and is situational. I recommend trying them all and picking your favorite for yourself.

This was my first guide and it was pretty fun to make. I hope it helped you, if not let me know what I could include and I'll add it in. Feedback is always great. If you have any questions feel free to comment them and I'll do my best to answer them. Goodbye and good luck everyone.