Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
Pros / Cons
It Deals high damage in ARAM.
You can keep long distance against enemies.
Can one shot any carry with full build.
Can't get close to enemies.
Using Basic Attacks and Q to deal damage is risky(just don't).
Teammate's low trust.
You don't need boots since your E cooldown is really low.
Why Youmuu? You need armor penetration for his ult,since it deals AD damages, and this items works well with it.