Well, first off, I would like to say this is my very first build... So constructive criticism is for sure welcome.

I would like to mention this is not a "Follow this build exactly or you will die" kind of build. Of course, there may come a time when u might need to switch items around, or get a completely different item, and thats okay ;) or of course if you just feel like it xP

Pros
Slow
Stealth
Scouting ability
Able to escape with Ambush
Tons of damage

Cons
Squishy
Easily countered by Wards/Oricles
Will be focused
CC screw you over

Exhaust - Another slow? A blind? Good escaping/chasing Ability? Why not?!

Flash - Another good way at getting close enough to your target to use your expunge? Getting more poison stacks? Getting that last hit you so desperately need after Expunge failed to kill?
Then this is the perfect spell for the job!

Cleanse - Good in case your not so sure about your ability with Twitch or just want to get rid of those pesky Teemo blinds, snares, taunts, you name it.

I tend to go with Exhaust and Flash, but go with whatever you feel you need to succeed!

Most people like to get Ambush, but be warned... Summoners who take an inexpensive item or no item at all, can easily grab a Sight Ward and set it up in mid brush, which can then get you killed if your scouting the brush for your team when your going for First Blood. Happened to me twice >_<

My choice for my skill distribution is because I want good early game damage with Expunge Expunge. I also don't like having a 10 second stealth so I like to mix that in with the slow, alternating between Ambush and Debilitating Poison.

I like start my game off with a Doran's Blade

Then I like to save up my money for a B. F. Sword for damage for easier killing/farming

Then I get Boots of Speed for an increased survivability and have a better chance getting kills

Then I get Phage for an increase in survivability, the damage, and the slow

Then I finish my boots with Boots of Swiftness most games, if they have quiet a bit of Crowd
Control get Mercury's Treads, or a lot of DPS get Ninja Tabi. You don't need Berserker's Greaves because you get enough Attack Speed from your Ambush.

Then I finish The Black Cleaver.

Now is the time I like to get life steal. I like something cheap because all the items are
expensive, so you could get Executioner's Calling, Emblem of Valour Emblem of Valour, Bilgewater Cutlass, or
Wriggle's Lanturn. If you get the Emblem, I advise against building it into a Stark's Fervor because the debuff can let the enemy know when your around and scare them away for your ganking.

Then I like to finish up my Frozen Mallet for the health and slow.

And thats pretty much my Core Build.

After that, I like to increase my Survivability more by getting Banshee's Veil, but if I'm doing well, I'll get Catalyst the Protector Catalyst the Protector, and get Madred's Razor Madred's Razor, finish Banshee's Veil, then finish Madred's Bloodrazor. Next, which I highly doubt you'll get this far into the build, get some extra damage / life steal by getting The Bloodthirster, and selling Executioner's Calling.

This is my build and I've had many successful games with it. Don't believe me? heres proof!!!

I would like to say even though Twitch has the capability to get every kill you and your teammates go for doesn't mean you should. Doing so could hinder your teammates ability to do well.

Also, if you notice the enemy has put wards down, ask someone to get an Oracle's Elixir or Sight Ward Sight Wards (or just do it yourself though you may lose the elixir soon because the enemy should be focusing you as soon as you show yourself) to destroy their wards so you won't be killed when your scouting. Or if the enemy has taken the liberty to buy an Oracle's Elixir, ask your team to help you gank them or focus them first in team fights

Be sure to use your manners by saying please and thanks!

One trick I found playing Twitch is if you use Ambush, and immediately after, start teleporting back to base, you will go invisible and still teleport :3 Good to use if u just got out of a team fight your team lost and u don't want to run far :D

I've read this somewhere but never put it to the test... If you use your ultimate and attack a tower, you can hit it out of the towers range.

After obtaining B. F. Sword you can 3 hit the caster minions. Whenever a new wave comes, focus them down. I wouldn't advise using your ultimate to farm a wave, unless your turrent's almost down, you have no minions at the tower, and your the only hope it's got. It may save the tower... But for the most part, DON'T DO IT!

And this is it... The end of the build...Thank you for visiting and reading my guide :D. And remember, this is my first build so please point some things out that I should be aware of.

I may add more details, but for the most part, this is indeed it!