Twitch's ult allows for his shots to pierce through his targets and deal damage to champs/minions behind his target so I thought why not buy a runaans on twitch because that way his ult will be firing 3 shots that pierce through targets. Many people will argue that runaans is a terrible item and that it has no real purpose besides farming like crazy but this build would be pretty stupid without the runaans. Each item in this build has a reasoning behind why its in this build and I will explain each one.

Runaans-spread out ult and gives you a lot of attack speed
Divine Sword-the activation ability in the SOTD works with twitchs ult and runaans so you'll be firing 3 critical strike shots that pierce through your enemies and the runaans will spread your shots to 2 additional targets
Blood Thirster- BT deals the second most damage in the game and it gives you lifesteal which will give you a bit of sustain (also since a crit shot is 200% of your damage you need to have high dealing damage items for crit shots to be useful)Infinity edge- Increases your crit damage
Berserkers Greaves- Just basic adc boots nothing special
Frozen Mallet- slowing for the cowards trying to run away and it gives you a lot of health so it adds a bit more sustain to you (frozen mallet can be switched out for BOTRK if the enemy team is stacking health or Black Cleaver if they're stacking armor)

Pros: u will deal massive damage and you have the capability to end team fights in 3 shots
Cons: very low sustain and defense if you are targeted u will die easily, also when your SOTD is on cool down there is not much you can do

In team fights never engage and never get caught by yourself since you are really squishy
To get insta-penta wait for their team to group up and activate abilitys in this exact order
Step 1. Activate Q to sneak up on them and gain bonus attack speed
Step 2. Activate Ult
Step 3. Activate SOTD
Step 4. Fire 3 basic attacks and BOOM istant triple kill and maybe penta
Step 5. Expunge the mo-fos that are still alive