Not Updated For Current Season
This is a guide for somewhat experienced players, although this build will work with anyone. If you are farely agressive then this is the twitch for you. After testing this build multiple times, I've never seen it fail. Follow this guide and you will become one of the most feared Twitchs out there.
-Twitch can become invisible, making easy to escape or gank
-He has a lot of attack speed without any items
-If you position yourself well you can get a pentakill
-He has slow
-He is has a ranged attack
-Ultimate can hit everything it passes for 100% damage that applies all on hit effects and criticals. (If you crit the person it hits first, then the whole bolt crits everything it hits. If the person hit first dodges, then the bolt will be dodged by all the people.)
-An oracle can make you useless
-You are always going to be focused
-You are tottaly item dependent
1. Buy a doran's blade and a health potion, that will give you some extra damage and more survivability.
2. Buy 2 avarice blade and 1 boots of speed the sooner you can, that will give a reasonable movement speed and you'll gain a lot of extra gold and 24% critical chance.
3. Now you should buy a berseker's greaves, it's one of your most important items, since it's your only attack speed item until you get your phantom dancer(if you follow build 5a).
4. When you can, buy an executioner's calling, it will add 18% critical chance(making you have around 45% critical chance)and will be your lifesteal item, letting you take dragon or elder lizard easily.
5. Now the build splits up a little depending on the other team:
5a. If the other team has 0-2 tanks this is the build you should take because it will make you destroy anyone with less than 2000 health in a matter of seconds. First buy a B.F Sword, and when u get money make into a Infinity Edge(If you followed this build this will be your main item, it will make your critical do A LOT of damage and also it will let you with more than 50% critical) and afterwards buy a phantom dancer(this will give all the attack speed you will need for the rest of the game, some movement speed, the rest of the critical chance you needed and some life saving dodge). After you buyed your infinity edge sell your doran's blade.
5b. If the other team has a lot of tanks you should buy a madred's bloodrazor and a black cleaver, and selling your doran's blade, that will give you an attack equal to 2-3% of your enemies health because or their magical resistance and a lot of armor penetration, since you'll get all of black cleaver stacks easily whit your ultimate.
6. Now sell 1 of your avarice blades and buy a bloodthirster if you followed the build 5a, with that you'll be hitting at around 700(counting your critical or your madred's bloodrazor) and with your ultimate's attack speed bonus and ambush's atacke speed bonus you'll be attacking at least 2 timer per second. If you followed the build 5b you should get now a infinity edge.
7. Finally sell your other avarice blade. Now here it will a personal decision what to buy but I usually buy another bloodthister or another phantom dancer to replace the critical chance I lost from selling the avarice blades(and also getting a little more atack speed).
Spray and Pray>Expunge>Ambush>=Debilitating poison
You should get ambush as your first skill, so if you're laning bot or top you can check the bushes for possible ganks, or to try to surprise someone in the bushes. If you're laning mid you should get ambush to try an early first blood that i'll explain later(if the person that is laning against you doesnt have any escape mechanism he will certainly die).
Now you should maximize expunge, because that will be your last hit, and surprising spell. It usually happens when u are ganking a stronger opponenet that he will try to kill you, so let's say that you end up with 200-300 hp and your enemy with 500-600, and he has 6 stacks of deadly venom and you have level 5 expunge. He's sure he will kill you so he won't run away, but then you use expunge him, that will kill him or let him with less than 100 hp, then you're able to finish him with ignite or you can just land another 1-2 hits. When you're ganking, also try to land all 6 stacks of deadly venom since expunge range is really huge. Also if you and your teammates are ganking someone, and he's already dead but you're worried someone will steal you're kill, just use expunge and get yourself a kill.
One thing people always ask me is why I maximize ambush instead of debilitating poison. Debilitating poison at level 1 gives 2.5 seconds slow and at level 5 gives 5.25 seconds, but how you got exhaust as a spell you'll have extra 3 seconds slow, more than you need, and the cooldown diference between level 1 and 5 doesnt really makes a difference in my opinion. If you took the build 5a then ambush is one of your most important sources of attack speed, since at level 5 it gives 100%, and also it's easier to scout or follow someone on the enemy team with more time invisible.
Spray and Pray gives you a lot of melee atack range and atack speed, and you will do damage to everyone in a line, so in team battles you should try to position yourself behind the enemies with at least hitting 2 enemies with your ult.
21/9/0, you're tanking the offensive masteries that increase your damage your critical and improve exhaust, and for the defensive masteries you'll take 4 magic resistance and 4 armor, you'll also get 2% dodge and nimbleness, that can save your butt a lot of times, because you can't become invisible when you're tanking damage, so for an example, the enemy team comes to gank and you use ambush, so they start atacking you so you can't become invisible. If you dodge 1 hit it will give a movement speed boost letting you become invisible and escaping.
9X Greater Mark of Desolation give you with the mastery sunder 23,64 armor penetration, being that all you need against a non-tank character.
9X Greater Glyph of Furor gives you with your infinity edge and the mastery lethality 267% critical damage, so if you're hitting 300 with normal attacks for an example you'll hit 801 with a critical hit.
9X Greater Seal of Evasion gives you 28,75% dodge chance with your phantom dancer and your evasion mastery, more than enough to get your nimbleness going.
3X Greater Quintessence of Fortitude will give your early game survivability along with doran's blade, giving you 217 extra health.
You should always try to get mid, so it will be easier for you to farm and gank bot and top. If you can't get mid you need to go bot, because it's closer to dragon. Here I'll give some tips on what you should do on the game:
If you got mid then you should try to get a first blood as early as level 1(normally you're going against ashe, teemo os someone like that, so they don't have more than 500 health). You should wait in the outer tower, and when your creeps reach you, use ambush. Then the creeps will start fighting, and the enemy champion will think that there's still no one in the lane and will advance a little. That's where we strike. Go behind him so when he flees to the turret you'll still catch him, but not to behind so he'll just flee to the bushes. Try to wait the 20 seconds until ambush ends so you'll get the full attack speed bonus. When ambush ends land 1 hit on him then use exhaust with ignite in him(so if he uses heal or a potion it will do reduced heal)and strike him as much as you can, usually giving you a first blood. But remember, if you're going against someone like mordekaiser or anyone with more than 600 health, he'll probably be able to get away with less than 100 health, and you shouldn't try to follow him into the enemy turret, because that way you'll surely die and maybe not even getting the kill. If that early first blood works now you'll be controling the lane, and when your enemy returns you'll be around level 4. Try to harass him around, landing some hits, and if you get more than 3 stacks of deadly venom on him you can expunge just to harass. If you get him below half his health, you should go stealth and try to kill him again. Now when you get level 6, you're able to gank anyone in the map. Just tell your friend in another lane to initiate, and then you just use your ultimate and hit the both of them, and when you can't atack them anymore, use expunge and get yourself a double kill.
You should continue creeping in the middle lane(not just ganking other lanes because that will let you short on levels)until you're at least 11. By then you should already have at least 4-5 kills and farmed really well. With that you should already bought your executioner's calling, and if you havent taken dragon with a teammate yet now's the time. Just use ambush and go to him(the farthest away you are from him, more time you'll have your ambush on and you'll have increased attack speed bonus, making it easier to take dragon down)and after he has 6 stacks of deadly venom expunge him, making it easier to kill him. Also try to always have a elder lizard buff with you, making even harder escaping from you.
With all the extra money of dragon, and all your kills, by level 15 you should already have all your core items, and you're owning. Now just have fun and wait until the other team surrender ;P.
Other items that could work on twitch(not my favorite choices)are these:
Last Whisper: if you're having problems making money, and there are lot of tanks in the other team, then you can buy this.
Guinsoo's Rageblade: some people like it because it gives you some attack speed bonus and also makes your expunge do some extra damage.
Banshee's Veil: if you're having a tough time and their are a lot of disablers on the other team you should buy one of these, saving your life many times.
Frozen Mallet: if your enemies are always escaping from you and you're needing some health then this should be your option.
Sword of the Occult: I ussually don't like doing this because it's a gamble item, because it can give a lot of damage for a small price, or low damage for a high price(early game), but if you like it then you could buy it.
Items you SHOULDN'T do:
Atma's Impaler: a waste of money with twitch, because you're not looking for armor, since you already have a pretty good basic one, and there are a lot of better items you could get the criticals strike from, and the 2% extra damage from your health is totally useless(it will give you like 40 extra damage).
Hextech Gunblade and Trinity Force: some people told me to include this item in my build because it will give a little damage a little ability power, some life steal(just the Hextech Gunblade) and some critical chance along with some attack speed(just the Trinity Force), but it is really expensive and won't make a real difference for you, since you don't need AP (late game you think that your expunge dealing 700 instead of 640 will make a difference?).
Sunfire Cape: please, don't stack sunfire capes and just keep running around your enemies, because just one oracle will completely end your game.
Malady: it was a really good item, but since the update they took the life steal away from it, making it useless at my opinion.
Good teammates for twitch:
Amumu: his ult will stun your enemies in an area, making it easy to you hit more than one enemies with your ultimate.
Galio: for the same reason as amumu, his ultimate taunts all enemies in an area making it easier for you to hit multiple enemies with your ult.
Janna: she helps your team supporting, but mainly because of her skill Eye Of The Storm, that gives you 50 extra damage and a shield.
Kennen: his ult stun the enemies around him, making it easier for you to hit multiple enemies.
And any other support and initiater, like Blitzcrank, Soraka, Shen.
Bad enemies fo twitch:
Mordekaiser: in my opinion is the worst champion twitch can face for two reasons. His shield makes it really difficult to kill him, and when he uses his ult on you, you're not able to become invisible until it's over.
Corki: he is annoying against any stealth character, because his Phosphorus Bomb will reveal you.
Galio: if he catches you in his ult along with some of your allies, you'll kill them and you as well, since you'll do a lot of damage.
Any other champion who has stun, disable or silence can annoy you, like, Taric, Amumu, Fiddlesticks, Rammus.
Sorry if there are any english errors since i'm Brazilian, and I would like any constructive feedback. Good luck and have fun with this build :).