This build focus's on massive amounts of movement speed and tones of splash damage in teamfights. You may find this build hard to use because it is pure damage and has no defentive armour and low survivability, but having high movement speed and Ambush allows Twitch to get away verry easily and makes for a great "backdoor" champion.
When playing as Twitch allways ask you team if they would like to invade. Twitche's Ambush allows him to facecheck bushes without the enemies noticing so Twitch can be the first player in.
This rune setup allows twitch to sneak up on enemies and assasinate them without knowing their getting killed untill they see their death recap.
Pros / Cons
PROS: This build gives Twitch an overall high damage base, and a large amount of attack speed which allows him to take out a turret early with one minion wave. Tones of splash damage with Spray and Pray and Tiamat.
CONS: This build has low survivability which makes him very squishy, but once u arrive in team fights and if the other team does not focus you, the fight is in the bag for you're team.
When farming hit all minions with you're passive then use Expunge for great splash damage.