Well this is my second build/guide I've done and the first one I've actually tried. I'm still not sure how to do all the fancy text stuff so I hope this is ok for you :P. Ok so I've mained Twitch since I started playing. He was free the week I started playing LoL and I've loved playing him ever since then. I've tried different builds and different playstyles from AP Jungle to just regular ADC and pretty much know everything about him. This build I'm doing is my main build I use which is basically a lot of crit/attack speed/and just beast-mode-on damage.

NOTE: IF THIS BUILD IS SIMILAR TO ANY OTHER TWITCH BUILD IT A MERELY A COINCIDENCE, THIS IS THE BUILD I'VE FOUND ON MY OWN FROM PLAYING TWITCH SINCE LEVEL 1 WITH COUNTLESS ATTEMPTS AT USING HIM TO HIS FULL POTENTIAL

For Twitch's runes I use

Seals: Flat Armour
Glyphs: Flat MR
Marks: Attack Damage
Quints: 3 Lifesteal

Pretty standard ADC runes with Lifesteal quints for a little extra sustain

For Twitch's Masteries

Like his runes they're pretty standard 21/9/0 ADC masteries.

Twitch's Items

Ok the core items I get on Twitch are Statikk Shiv, Berserker's Greaves, Infinity Edge, Phantom Dancer, Bloodthirster, and a Runaan's Hurricane.
(Here I'm talking about core items)
Here's why:

Statikk Shiv:

I like to get a Statikk Shiv as my first core item because of the Crit/Attack speed + the passive on it is good for harassing. Also the movement speed makes twitch so much more versatile in his Ambush form.

Berserker's Greaves:

No explanation needed here. These are just pretty standard ADC boots with attack speed that will help you get more hits on the enemy to do more damage with your Expunge.

Infinity Edge:

The reason I get an Infinity Edge as my 2nd "big item" is how much extra damage it gives you. If you hadn't realized by now I like my Twitch to have a lot of crit, and with the 250% crit damage his damage output is just crazy.

Phantom Dancer:

I feel that getting a Phantom Dancer on Twitch is a necessity. With the movement speed, crit, attack speed, and ignoring unit collision, this is just a beast item on Twitch and makes him one scary **********er when he goes into Ambush.

Bloodthirster:

Bloodthirster is one of those items I just think is amazing. It gives you up to 100AD and 18% Lifesteal with its passive fully stacked. The AD is really helpful to burst enemies down easier, and the lifesteal gives him some much needed sustain.

Runaan's Hurricane:

I finish up my build with a Runaans, an item that most people I know don't like, and say it is not very helpful since it only gives attack speed....wrong, I love this item on Twitch because it applies on hit effects which makes his passive apply poison to 3 PEOPLE AT ONCE! That's 3 people you can burst down with auto attacks then destroy them with your Expunge! This is definitely one of my favorite items on Twitch.

Twitch's Skill Sequence

On Twitch I get a point in my Exupunge (E) 1st and then proceed to max it out. I max out this ability 1st because of how much burst damage it does. This is the main ability I use and is great for harassing.

The 2nd ability I get is Twitch's Venom Cask (W). I only get 1 point into this at level 2 and then max it out last. The reason I only get 1 point in it is for the extra 2 stacks you get when you land your Deadly Venom.

The 3rd ability I get is his Ambush (Q). I pick this up at level 4 and then max it 2nd right after Expunge. I get this after Venom Cask but max it before because I feel that the 2 extra stacks are more important very early game, but the invisibility with extra attack + movement speed is more important early - mid game.

The last ability I get is obviously Spray and Pray (R). Hopefully no explanation needed, I put a point into this any chance I get.

Summoner Spells

More standard ADC stuff.
Flash: Is a spell I always use regardless of the circumstances to reposition in fights and to get away easily. Not much to say here.

Barrier: I use this spell for the shield (obviously) and because you don't really need any other spell on Twitch. I've seen people use Ignite and just wonder...why?!? Twitch has Deadly Venom and Expunge to secure kills and that's all Ignite is used for...to secure kills.

Cleanse: I Sometimes use Cleanse but it is purely situational, if they have a team with hard CC for example

Here are some of my games with this build

Lol idk

Just a little trick to do with Twitch is to go into Ambush and then recall. Not to crazy but it can be pretty helpful to recall invisible. [*] Note: You will not stay invisible for the entire recall until Ambush is level 5

Not really a trick but the way to do the most damage with Twitch is to use Ambush, throw a Venom Cask, get a few auto attacks on, and then Expunge when you're at max Deadly Venom stacks.

Well that's it...

Hopefully this guide could help you. I know it's not the best one since it's only my 1st one but I had to start somewhere :P. If you think there is anything wrong about this guide or you think you have something better to add, feel free to leave a comment, constructive criticism is appreciated, but no mindless hate pls. I know this is late season 3, but when season 4 comes I will make another with the new masteries/items. Thanks for taking your time to read this and Rate up if you liked it. :)))