So I played some Dragon Priest today in standard and was cleaning house with all the Shamans and C'Thun druids I played against.
Thoughtsteal is legit amazing against these guys. Same with the 4/3 for 4. Those are just awesome ways to take their stuff and keep your hand full so you can use Twilight Drake more effectively.
The dragons give you powerful drops at almost all mana levels (2/3 for 1, 2/4 taunt for 2, 3/5 for 3, 3/6 taunt for 4, etc), combined with the ability to heal after trading, and Holy Nova actually having a chance at killing something again, the deck is OK! Surprisingly good even.
2x Deaths to handle the Shaman 7/7s. To be honest, if you don't have death for that guy you probably lose. So in that case its in the same boat as every other class, but hey the priest answer only costs 3 mana instead of 4 or 5. Overall against Shaman you're probably ok if you can get a taunt or two out before the 7/7 shows up or be able to kill it immediately with Death. Then Holy Nova or Excavated Evil cleans up the rest of the aggro and your dragons roll in to mop up.
Against Druid, you could run 1x Shadow Word pain to deal with Fandral Staghelm, but I still think Shadow Madness is more useful overall. Death makes short work of the Arakkoa and C'thun when they show up, and your big dragons and Taunts will get you good enough trades to get out a big minion or two which Druid won't be able to remove. Then you just heal and thoughtsteal their best cards and GG. Stealing their C'thun will probably get you a Trolden highlight or something, but most of the cards are pretty good. Definitely want 2x Thoughtsteal against Druid.
The deck seems really playable against the two most common decks I'm seeing atm (Rank 10-9 and climbing)
