This build will help you with a full damage output build. Your rune choices are basically for your survivability because of Twitch being so squishy. The masteries is just a compliment to your early and late game. The items are full damage and should kill anyone fairly quickly if played twitch right. When your build is finished, you could and i do recommend replacing your boots with Phantom Dancers. The skill sequence is focused on your expunged most for early game ganks for your expunge will finish off enemies if they are fleeing. Your ignite and poison should do enough damage over time that by the time u have enough stacks of deadly poison on yor enemy, you'll be able to use expunge to finish them off. Ghost is just a away for you to travel quicker to your enemy's incase of tower pushing or a team fight. You could also use exhaust and flash or ghost and exhaust. Your summoner spells are mostly your choices though, and you should build your masteries according to your summoner spells. Basically as Twitch you want to gank early game and get fed. Harassing is key but if you opponent has range on you try to farm more than harassing. Your vampiric septor should keep your health up while you are laning so taht you dont have to recall so often. By the time you are working your way to a frozen mallet, your damage output should be very large. When ganking, try to stay behind the enemy stealthed, and wait for minions to be in range of your spray and pray so that you can use spray and pray to life steal minions while killing the enemy.