Hearthpwn

Used this deck to aquire Legend this season.

Priest seems to be the worst class in today's meta and frankly speaking, I don't know why. Going big you have quite a good matchup against many popular decks: Big Warrior, Pirate Warrior, Libram Paladin, Alignment Druid, Quest Rogue. Also aggro matchups are winnable, unless they have very good hands and you don't. Weak matchups are mostly Warlocks or other OTK decks (Mage, DH), but they seem to be not as popular right now.

Basically what you want to do is play Vanndar Stormpike and/or Dark Inquisitor Xanesh as soon as possible and get cheap big minions - preferably drawn with corrupted Insight to make them even cheaper. Then after they are killed fill your board easily again with Carnival Clown, Amulet of Undying, N'Zoth, God of the Deep, Y'Shaarj, the Defiler. Use removal spells, Shadowcloth Needle and Mind Spike to stay alive.

Card choices:

Raise Dead - only 1 copy as 2 is often too much as you don't want to play it early and you don't want to play it when low on life. Ocasionally you get N'Zoth, God of the Deep, Y'Shaarj, the Defiler or corrupted Carnival Clown with it and you are very happy. Also good topdeck.

Call of the Grave - sometimes you need cheap shadow spell to activate Shadowcloth Needle, sometimes early deathrattle minion, sometimes 1 mana (or free) deathrattle effect. Only 1 as although this has some flexibility, it's still random and might not give you what you need at the moment at all.

Insight - one of 3 cost reducers, absolutely crucial card, never cast it uncorrupted

Shadowcloth Needle - anti-aggro tool, this deck plays plenty of shadow spells

Amulet of Undying - keep it on starting hand and trade on the first turn. You can trade it more than once, but most of the times res 2 creatures is enough

Devouring Plague - great early removal with lifegain to stall on these early turns. Also one of early ways to corrupt Insight

Palm Reading - very versatile (you'll rarely get nothing useful from your options), only way to get spells outside of shadow school, another way to corrupt Insight

Hysteria - great, flexible removal, your opponent will rarely have time to play around it and just won't do so. After few cost reductions are made you can often clear board with it and make your own the same turn

Vanndar Stormpike - while you can win without him, he makes you able to do some degenerate plays like going corrupted clowns turn 7. Playing him turn 4 (3 with coin) is almost always good and wins you many games.

Void Shard - another anti-aggro tool that makes you live long enough to execute your game plan. One of few lifegain options for shadow priest.

Dark Inquisitor Xanesh - similar role to Vanndar Stormpike, doesn't require cards to be in your deck and works for Insight too, but offers lower discount, not for all minions, costs more and has arguably worse stats. Better for early rise dead than Vanndar though.

Darkbishop Benedictus - just another... anti-aggro tool? Well, yes. Turn 2 deal 2 seems to stop many decks for long enough to survive and is worth even losing ability to cast Renew

Fleethoof Pearltusk - 5 mana 4/4 rush is not a good card. 0 mana 8/8 rush is. Also only minion that prays to both N'Zoth, God of the Deep and Y'Shaarj, the Defiler.

Lightshower Elemental - one of two Amulet of Undying targets, also resurrected by N'Zoth, God of the Deep. Cast early even on full life and res many times.

Soul Mirror - best removal, use wisely (also can make additional N'Zoth, God of the Deep/Amulet of Undying/Y'Shaarj, the Defiler targets, but can also litter your res pool

Mo'arg Forgefiend - quite good to play turn 8, insane when you can do it turn 5. Another Amulet of Undying and N'Zoth, God of the Deep target

Carnival Clown - although you can play it as 3 4/4s turn 9, this deck can reduce them to seven 2 mana 4/4/s turn 6. Clowns are not a focus of this deck though, it is just one of waves you send to sink your opponent

N'Zoth, God of the Deep - this deck plays only with 3 minion types, but this should be enough. Sometimes you can cast him turn 7 and already resurrect 2 minions, sometimes it's worth to hold on

Y'Shaarj, the Defiler - refil your hand with corrupted cards, draw more creatures with Insight, rush oppponent minions with 8/8s and build a wall or 4/4s. No Tickatus though :( Also, if you start with Carnival Clown in hand and don't draw Dark Inquisitor Xanesh, this is the only way to corrupt them

And that's it. No Moonfang with buffs, no Mr. Smite, tried it all, but it seems to do best when built with more defensive approach in this meta. With Fractured in Alterac expansion this might get even better with Xyrella, the Devout and Undying Disciple looking like worthwile additions.