This deck is from Blizzard’s Off-Meta Spotlight, here’s what they had to say about it:
Quest Priest – 71.4% win rate/63 games
Up next is a Quest Priest variation that looks to take advantage of Priest’s ability to take games into later turns, with the burst potential granted from the Legendary Prophet Velen. This deck has ways to play tons of cheap Deathrattle minions to help assure the completion of Awaken the Makers. Once you have obtained Amara, Warden of Light and set your health to 40, Shadowreaper Anduin and a pair of Mind Blasts turn on the aggression to end the game.
The best version so far. Worked well for me with alexstrasza and Rotten Applebaum instead of Arzus and Prophet.