Gain increasing amounts of AD or AP, Adaptive over the course of the game.
WhyPress the Attack
Press the Attack massively ramps your damage, especially when looking to come out of [Q] stealth and assassinate a target. The extra burst and amp will make your [E] hit like a truck.
Triumph acts as a largely mid-fight heal for late game teamfights where you are able to hit the majority of the enemy team with [R].
Twitch is an AD Carry that naturally relies on getting as many auto attacks in as possible for extra damage. Alacrity will also help you build passive stacks faster in the early game for [E] burst damage.
WhyCoup De Grace
Coup De Grace is the go-to rune for reliable bonus damage. Paired with the burst of [E], Twitch's damage can scale incredibly well with a small lead.
If you're playing into a number of tanks (Jungle, Top, Support) Cut Down can be a great alternative thanks to your ability to hit multiple target in a teamfight with [R].
Celerity is a naturally strong rune on most Crit AD Carries as the bonus Movement Speed synergizes well with your Zeal items.
Gathering Storm is your late-game insurance policy. In a 40min+ game you will be bale to potentially take over a teamfight with a well positioned [R].