Hearthpwn

I've started with standard control dragon and changed the win condition of 2x mindblast + alex for 2x Divine +1x Topsy.

Then i add 1x Stormwind Knight to get an OTK. (-1 Holy Fire) 

Stormwind Knight + Power Word: Shield + Power Word: Shield + Divine Spirit + Divine Spirit + Topsy Turvy = 36 dmg

Somewhere along the road i figured out Shadow Madness is almost as effective as Stormwind Knight and can also be assembled through Shadow Visions so now i run one of each. (-2 Holy Fire)

Shadowreaper Anduin was too slow and somewhat irrelevant in most of my games because they ended most likely around T9~T12 so he had to go. Firetree Witchdoctor is good in Mind Blast priest since she is versatile and can get more copies of dmg spells but i believe Loot Hoarder performs better in combo decks. -1 Scaleworm +2 Dead Ringer

If you stop right here the deck is already solid. I've made many modifications from this point onwards but i can't tell which variation performs better. For example, you can definitely cut more cards to make room for Bloodmage Thalnos+ Spirit Lash if you are facing a lot of Paladins.

Short answer: you should play Hunter.

But if you don't want to be part of the scourge (hey, tempo storm said it, not me) and wish to purge it instead, Priest got your back covered. Just as in real life, Priests are very good at exorcising evil things. Now all is left is to choose your path: The Bruce Lee way or The Chuck Norris way.

Mind Blast Priest is the Bruce Lee way. We give them many punches until they don't move anymore. Very effective vs decks that hits their own faces because now we don't need to deliver as many punches. Examples are Odd rogue and Warlock.

Divine/Dragon Priest is the Chuck Norris way. Out of nowhere, just one BIG kick in their face, D-E-A-D.

Mind Blast Priest was very strong and botton tier 1 deck when Cubelock ruled over the meta. With the rise of Hunters, Warlocks are being hunted and by now almost extinct. So its just natural Mind Blast Priest fell into a tier 2 spot.

Divine/Dragon OTK on the other hand, is faster then MB Priest and punish oponnents that do not trade into minions, but is weaker vs Taunts. The big Taunt class was Druid and his era has ended. Hunters in general do not want to trade and they have only a few handful taunts. So yeah, Chuck Norris that Hunter.

The most basic lesson in Chuck Norris Priest is always remember how to perform the Roundhouse kick:

Stormwind Knight + Power Word: Shield + Power Word: Shield + Divine Spirit + Divine Spirit + Topsy Turvy = 36 dmg

Important Tip to not look like a fool: Always double check if all cards are assembled AND if there is enough mana to pull off the combo.

Hunter: Try your best to save Duskbreaker to answer Lesser Spell Stone. Against beast hunter you should play Duskbreaker to wipe the board as soon as possible.
Against Rattle/Recruit Duskbreaker main role is yo buy time for Psychic Scream. Always check secrets before performing the OTK and COUNT if they already played both copies of Freezing Trap adn Wandering Monster secret.

Priest: Search for combo pieces very aggressively. Try to save Shadow Visions for when just one part of the combo is missing. Play Twilight Drake as a stand alone minion, most efectly in the turn after a Psychic Scream was played or if he is already in lethal range.

Mage: Save Pws and Shadow Visions to check for counter spell. Only 1 Topsy OR Inner Fire can be used instead. Against Control mage, save a removal for the Lich King.

Warlock: Steal or Scream Void Lords.

Paladin: Double Duskbreaker is your best bet to survive vs token decks. Teching in Spirit Lash helps a lot. Not a good matchup otherwise. Deck has a great winrate vs OTK paladin, try to set up Twilight Drake on T8 since on T9 Uther of the Ebon Blade is usually played and he will be defenseless.

Shaman: Duskbreaker on curve and win or die fishing for him. Giants are a pain in the ass to deal with, but Shaman can't really recover the board once behind.

Druid: Versus Mechathun Druid there are 2 ways to win. Play a big Twilight Drake after they played most of their cards (they can only Naturalize once but we have 2 drakes) OR send 2 minions to their deck through Psychic Scream and let them fatigue. (2 Acolytes work best)
Mechathun will be played eventually so steal it with the cabal combo. Taunt druid is a lost cause. Malygos Druid is a race to who assemble the combo first but i believe this deck is faster.

Always keep Cleric. Keep PWS only if Cleric is already in the starting hand. All other cards are situational.

Hunter: Duskbreaker, Acolyte of Pain, Twilight Drake, Dead Ringer, Loot Hoarder.

Priest: Topsy Turvy, Shadow Visions, Shadow Madness, Stormwind Knight, Divine Spirit, Twilight Drake

Rogue: Duskbreaker, Twilight Acolyte, Twilight Drake, Scaleworm, Acolyte of Pain, Dead Ringer, Loot Hoarder

Warrior: see Priest

Druid: Dead Ringer, Loot Hoarder, Acolyte of Pain, Topsy Turvy, Shadow Visions, Stormwind Knight, Divine Spirit, Twilight Drake

Shaman: Duskbreaker, Twilight Drake, Cabal Shadow Priest, Psychic Scream, Acolyte of Pain, Dead Ringer, Loot Hoarder.

Mage: Power Word: Shield, Shadow Visions, Acolyte of Pain, Dead Ringer, Loot Hoarder, Duskbreaker, Twilight Drake

Paladin: Duskbreaker, Twilight Drake, Acolyte of Pain, Power Word: Shield

Warlock: Twilight Acolyte, Dead Ringer, Loot Hoarder, Acolyte of Pain, Twilight Drake, Psychic Scream, Duskbreaker, Scaleworm