How to grind mastery on control fast?

I have recently ate control. I have all the moves (cuz I had eaten control way before the rework) except v. How do I grind mastery fast since it needs 350 to unlock. Also to upgrade it I need 500 mastery. Can anyone tell me a good method. I've tried server hopping bosses but it takes alot of time and I only get 2-3 mastery per kill. Any replies are welcome.