Hearthpwn

Hello,

First of all, thanks for reading this post. I'm French, so my English may not be great, I hope it won't be any disturbing. 

With Titans launch, i've experimenting a lot on Priest decks, because of some great new cards I wanted to try. 
It was pretty hard to get a good balance (too much spells and you only have reactive plays/don't get value from Cathedral of Atonement, too much minions and you don't get the ones you want from Creation Protocol/lose your Love Everlasting/don't get the answers you need).

I ended up with this version of Control Duplicating Priest I enjoy a lot. It's a 30 cards version so that you can get Love Everlasting early most of the time. 

I mainly play on mobile so I don't have accurate stats on this deck, but I sure win more than I lose, and am pretty sure i could have won more with better choices in some situations. 

Overall Gameplan
You have various gameplans, depending what you're facing.

The main idea is to duplicate some key minions.You have 3 ways to duplicate : Power Chord : Synchronize, Creation Protocol and Celestial Projectionist.

The minions you want to clone are the following:  

• Armor Vendor and Blackwater Behemoth when you're facing aggro
• Dirty Rat against combo decks
• Ignis, the Eternal Flame and Ra-den in control matchups
• Aman'Thul against pretty much everything

The rest of the deck is here to control games, and have some sustain.

Card Analysis

• Armor Vendor : here to have some cheap minions (always good to have a Cathedral of Atonement target), some sustain in aggro matchups that can be targetted by Celestial Projectionist
• Shard of the Naaru : key card against Mech Rogue and good against Pure Paladin, Warlock, and decks that run buff or deathrattle minions (like Plague DK for instance) in general
• Sir Finley, Sea Guide : great in two situations : 1) when you have your key minions in hand before having played Creation Protocol, you then like to swap them back in your deck; 2) when you are in a bad situation, seeking for a good answer
• Celestial Projectionist : wasn't hyped at all when it was revelead, but it ends up as a good card in this deck. That's the worst duplicate card you run but it combines well with Armor Vendor and Dirty Rat. You can also create a solid win condition playing it on turn 10 with Ignis to get two 10 mana weapons 
• Creation Protocol : key card of the deck overall that you keep at mulligan most of the time. You get 1 or 2 copies of you key minions (means the original one stays in your deck) that will be summoned by Ra-den. That's also your only forge card, to get your Ignis ready. 
• Dirty Rat : think wisely before playing it. It's a great card to disrupt your opponent win condition (Sif, Odyn...) or good minions in general like Titan Cards, but it can make you lose the game if you play it on turn two and give your opponent a big minion on board. 
• Power Chord : Synchronize : pretty much like Creation Protocol, great to have a second copy of your Behemoth or Aman'Thul
• Thrive in the Shadows : combines well with Love Everlasting. Helps you to dig in your deck for good answers. 
• Cathedral of Atonement : pretty much a good keep at Mulligan. You may target an opponent minion before silencing or Cannibalizing it
• Holy Nova : ok AOE. Helps to make some damage on Reverberation targetted minions. May be replaced by the Light it Burns if you're facing more single big minions than extended boards of little minions. 
• Love Everlasting : great card overall. You run a lot of other spells as well as Svalna, so you rarely end up not being able to play a single spell on your turn, even if you played Love Everlasting on turn 3. 
• Cannibalize : great single target removal. One of your only way to restore HP. 
• Ignis, the Eternal Flame : i like it more and more. Good to get a 5 mana weapon against Druid to put some 4 mana minions on board. Mainly used to get 10 mana weapons to close game (Windfury and Summoning 8 mana cost is a great combination; but gaining armor, lifesteal or dealing damage can be ok too)
• Shadow Word : Ruin : great against Rogue, Druid, Warlock. Way better than Serenity in the current Meta imo
• Clean the Scene : great AOE. 
• Ra-den : made a try with it but it ends up as a great card in this deck. Resummoning big minions, duplicated from your deck or discovered by Aman'Thul, is a great finishing move. Try to keep a Cannibalize or Shadow Word to instakill him the turn you play him. 
• Sister Svalna : not sure about it. Good for sure with Love Everlasting and in some matchups (mainly Priest mirrors), but may be too slow most of the time. 
• Aman'Thul : at this stage, it may be one of the strongest cards ever. All 3 abilities are great : making ennemy minions impossible to ressurect is great in some matchups (Warlock mainly), having a big minion with taunt and lifesteal is good (and you may want to copy it on your next turn) and copying a Behemoth is game winning. The legendaries you discover are also great value. Overall a card that feels totally overpowered and may get some nerfs. Just be careful against Mage and Reverberation. 
• Blackwater Behemoth : game winning against aggro, great to copy and then resurrect with Ra-Den. 

Cards that were tryied but not kept

• The Light it Burns : most of magnetised mechs and titans have more health than attack so it may not be as good now as it used to be. 
• Serenity : good against hunter but way worse than Shadow Word : Ruin most of the time. 
• Overheal package : fun but not good
• Whirlpool : too slow
• Harmonic Pop : it can be hard in nowadays Hearthstone to clean boards with 6 damages on turn 6 - pretty crazy to say that. Good with Love Everlasting, but I feel that's not sufficient. 
• Fizzle : you don't need more value
• Identity Theft : you don't need more value and that's slow. 

Matchups 

• Hard matchups against : 
  • Mage : mainly because 1) you only have an infused Clean the Scene to get rid of Elemental Inspiration 2) you could have hard times to Dirty Rat the opponent's Sif as he runs some other minions and 3) the early boards from Cold Case and Keyboard are annoying for you
  • Warrior : mainly because of Odyn, that you want to Dirty Rat, but may not be able to. An early Blackrock'n'Roll may be hard for you too
• Average ones : 
  • Warlock : depending of the version your opponent plays. An early Sargeras can be tough. Keep a Shard at mulligan to get an answer to an early Amorphous Slime.
  • Hunter : overall, you have all you need to resist it, but you may be on low HP pretty early and could face some difficult decisions. If you're able to survive until your Behemoth, you'll win most of the time.
• Good ones :  Pretty much all the rest. You can outvalue other Priests or Blood DK, even if VS a 40 cards version. You can resist to hyper aggro decks. 

Fun facts 

• Had a game against control 40 cards priest in which I got Defense Attorney Nathanos and made waves of minions discovering Ra-Den with him. Easy win eventually.
• Summoned 12 Aman'Thul during a single game.
• Discovered Al'Akir with Aman'Thul, buffed it with Cathedral, copied it with Aman'Thul and Power Chord : Synchronize, then crushed my opponent with a new wave of Al'Akir thanks to Ra-Den. 

Feel free to ask questions. I would be glad you give it a try !