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.
This is a quick guide on possibly the best way to build Riven preseason 6. The basis behind this build is the Essence Reaver's passive, which with Riven is the best thing since sliced bread. Basically: Crit gives you cooldown reduction. An Essence Reaver plus Cloak of Agility will give you a whopping total of 65 AD, 40% crit and 40% cooldown reduction for a disgusting amount of damage! Add the Mastery that procs with crit and you become an absolute monster.