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.
Ashe The Unknow Mid Build
Plentiful Bounty is useless. Care if you get 5 more g for a minion kill. Specc on it when you have to. And if you're meeting Heimendinger use volley on his turret.
When someone is running away take Frost Shot. Don't waste Enchanted Crystal Arrow if the target is on the other side of the field. Use it when someone are running away. Don't use Frost Shot on minion, just waste.