Not Updated For Current Season
Twitch Quick Silent Death
These set of masteries I have found to be the most useful. Adds a little extra damage while keeping the utility of a little extra XP also.
With Twitch the real key to being able to take down 2 or 3 opponents at a time is to move in stealthily, take out the weakest one first, then move on down the line. Working with your team is key in this. When all of the other team is grouped up have 4 of your team attack from the front while you from the rear. Also remember to mark the opponent to focus on. Many times I have seen 5v5s that end with one team completely gone and the other all almost dead but still all 5 up. This allows you to also take out support characters first like Soraka or Heimer.
I always take Ambush first as I am almost always mid, but either way it allows me to scout ahead before minions come out and see who will be in that lane with me. 20 seconds is really enough until you start to roam and gank. I usually start to roam at about level 10 or so. Expunge is a great tool at level 3 4 and 5 to harass whom ever is laning against you. Stealth in hit them 2 or 4 times, then expunge as they run away. At level 3 of expunge if you can get someone with 6 stacks of venom you will probably kill them with expunge. In all honesty though at that level people run far before you have a chance to get 6 stacks up.
Now at 6 I always take Spray and Pray, many people say its too slow to be useful at this level but this is just not true. Using stealth waiting until it is almost up then attacking using spray and pray, debilitating poison, then at 6 stacks expunge and if you need you can exhaust them right out of stealth if you need a little more time. But right out of stealth with spray and pray your attack speed should be about 1.2 at this level. Which is not very high for twitch but at level 6 it is enough to take someone down.
The rest of the skills after about 10 don't matter and rely mostly on personal preference. I choose to level debilitating poison last because at level 1 it does enough to kill most people, and with twitch I usually hit 18 fairly quick.
With runes you really need to decide first on what your play style or goal is with that character. With Twitch I like to move quick and get behind the other team so I always take 3 speed quintessence adds 4.5% more movement speed. With this the zerker treads, 20 stacks of the dagger and phantom blade I can catch up to any opponent with a speed of about 491. I only take one set of speed marks as Twitch will cap out at 2.5 with his stealth bonus at level 18 and with the items I will talk about in a moment.
Twitch runs out of mana really quick and his MP5 is fairly low. As such I take MP5 seals and mana glyphs. These help a ton in the early stages of the game.
Twitch is a character that requires understanding of what you want to accomplish in the end and understanding of when each item would benefit you more. I always start with vampire scepter. This item costs 450 and will not allow you to take any pots with you, but it also allows you to just attack to gain HP. Also if you get ignited early in the game or at any point for that matter it allows you to just attack a minion to keep you alive. When I first started to play my first instinct when my HP was low was to run away. With Twitch you have to reconfigure that thinking. You need to be able to judge if you stay and attack will you be kept alive or not. As soon as I have 1400 gold I will return to get Malady and right after it the Berserker Greaves.
From here on out it all depends on who you are up against. If there is a tank Garen I will take the Black cleaver next, if I had a slower start I will take Zeal next and if I already have a few kills under my belt I will take Sword of the Occult next. If I don't take zeal then it is always my 4th item as the speed increase helps a ton!
With Twitch the items you should never go without are, Milady, Phantom Dancer, and Madred's Bloodrazor. Just adjust the order for where you find yourself.
Overall Twitch is a very strong attack character. If you get focused by 3 decent players though you will not make it out alive. He is great for sneaking up on people and the best habit to get into is to, when you can, check the other players for Oracle Elixirs. Just when they come into view anywhere on the map. Strike swiftly and you should never have problems with 29/5/5s. Since I started playing Twitch I have only had one game where I died more than I killed. He can carry a decent team to victory but its always better to work together. Also as my closing note as soon as you find the weak player on the other team (IE the one always running off alone, or the feeder) go after him relentlessly.
Have fun with this little rat.
Play well my friends.