Hearthpwn

Greetings! Today I want to show you an awesome deck for a control priest.
Arcane priest is a deck that can easily counter almost any other Control deck (which there are almost none) and survive early agression of Aggro decks.

MULIGAN

If you don't have a coin you must muligan for Holy Smite, Wild Pyromancer or Arcane Anomaly with Power Word: Shield.

If you're going second then your choice should be: Arcane Anomaly, Wild Pyromancer, Holy Smite, Shadow Word: Pain or Power Word: Shield.

GAME PLAN
Against Control:

Try to get early advantage throw Arcane Anomaly by buffing and healing it. After first faze of the game you should use Acolyte of Pain (your main card drow source) to find Arcane Giant, Entomb, Elise Starseeker (with Golden Monkey) and Shadow Word: Death. 
Yogg-Saron, Hope's End isn't a win condition in this deck, but a card that can turn tables around when you desperately need it (or kill you).
Thoughtsteal and Shifting Shade in early part of the game may be very favorable.

Against Aggro:
When facing aggro you should get as much value of Wild Pyromancer as possible by using Holy Smite, Power Word: Shield, other low cost spells and hero power to control a board (but be very careful with it).
Use a Priest of the Feast as main healing source. You must use it with caution, because you want to milk as much value of it as possible (as from any other card).
Try to find Holy Nova.
After first half of the crystal bar you should find Arcane Giant and drop it with a reduced cost.