Hearthpwn

Thief Priest!
First of all, I don't recommend you to play with that deck on Rankeds, because it's a fun deck :D. However it doesn't mean it's not a good deck. It's a deck for someone who just wants to play with Priest to make some quests done or to have some fun. You can try playing this on ranked mode but I wouldn't do that :d. 

About the cards:

Crystalline Oracle, Mind Vision, Cloning Device, Seance, Curious Glimmerroot, Thoughtsteal, Devour Mind, Holy Water and Archbishop Benedictus - core, necessary thief cards,

Northshire Cleric and Bloodmage Thalnos - draw cards,

Spirit Lash - good removal. especially against Odd Paladin, which is in the meta now, in combination with Bloodmage Thalnos it can heal you even to full HP and of course better board clear,

Shadow Word: Death, Mass Hysteria, Psychic Scream and Shadowreaper Anduin - very good removals, especially against bigger minions,

Zilliax - very good card, played in most of decks, good removal, heal and defensive card,

Tar Creeper - strong defensive card in early-game,

Unidentified Elixir - might be useful in early-game,

and Elise the Trailblazer - not necessary, but good addition, more cards. You can put in second Mind Vision, Holy Water or Unidentified Elixir instead of her.

Enjoy!