Hearthpwn

A simple dragon priest deck I used to climb from rank 6 to legend this season. 

Stats

The strength of this deck is in it's ability to destroy the aggressive decks (secret paladin, aggro druid and zoolock) currently prevalent on the ladder with it's strong early minions and it's many board clears. However, this deck can also perform well against other classes and archetypes.

Mulligan

The mulligan phase for this deck can be very simple, as you are always looking for a strong curve in turns 1 - 4. Therefore ideally you will want to find Twilight Whelp, Wyrmrest Agent, Blackwing Technician and Twilight Guardian. Northshire Cleric and Brann Bronzebeard can also be strong cards to play in the early game if you're not finding dragons. 

It's important to be able to activate your dragon synergies early game, and thus it can be completely correct to keep Ysera or Chillmaw in the mulligan if the rest of your hand demands that you have a dragon in hand. Twilight Guardian is an ideal dragon synergy activator to keep as they will allow your strong early game of Twilight Whelp, Wyrmrest Agent and/or Blackwing Technician while still being playable on turn 3 or 4. 

I will keep Northshire Cleric despite it not playing to the dragon synergies as it can be a great way to fill out the curve if the strong early minions are not being drawn.

If you suspect that your opponent is likely to play very large minions very early (i,e, a handlock playing giants or an aggro druid playing an early Fel Reaver) you may consider keeping a Shadow Word: Death in the mulligan, but I would only do so if the rest of the hand allows for a strong early board.

Brann Bronzebeard?

Brann Bronzebeard is a powerhouse in this deck, with almost all minions having strong battlecry effects. Twilight Whelp, Wyrmrest Agent, Blackwing Technician and Twilight Guardian are all already very strong minions for their cost if you can trigger their battlecry, and each of these battlecry buffs are triggered twice with Brann on the field which can be game-winning if achieved early. Azure Drake will draw two cards, Shrinkmeister, and the strongest interaction in the deck being Blackwing Corruptor dealing 6 damage on being played.

Although Brann Bronzebeard has very strong interactions in this deck, he is not the only way the card can win the game, so you can play him on board as simply a 2-4 minion, but I would avoid doing so unless you have board control already. This is espcially strong on turn 3 if you can play him while he's protected by a Wyrmrest Agent, allowing you to follow up on the next turns with Twilight Guardian, Azure Drake or Blackwing Corruptor. Brann can also be saved in hand and used to combo with battlecry cards when you have a bit more mana to utilise. 

General Gameplay Tips

Against Aggro:

The key to winning against aggro is get a strong start on board using your early minions (especially the taunts). The combination of a strong board presence, many board clear options (Holy Nova, Lightbomb and Chillmaw) and the priest hero power put this deck heavily in favour against any aggressive deck. Simply fight for board presence whilst sustaining through any burn.

Cabal Shadow Priest is also very strong against many popular decks right now, as it can be used to steal Imp Gang Boss, Shielded Minibot, Keeper of the Grove, etc. Or can be used with Shrinkmeister to steal larger minions. 

Against secret paladin, it is important to use Lightbomb and/or Shadow Word: Death effectively in order to shut down a Mysterious Challenger turn. Lightbomb is usually the preferred removal of choice as it will clear the rest of the board, whilst leaving Shadow Word: Death for removal of Dr. Boom or Tirion Fordring.

Against Control

This deck is much less suited to winning against control decks, but that does not mean it is impossible. If you can get a strong early game curve you can become the aggressor and win games very early against a slower starter, with many strong minions in turns 1-4 and Holy Nova and/or Blackwing Corruptor as potential burn to push for lethal. 

In games that run longer, Ysera will become a very important card. If possible, Ysera needs to be played when you're confident it won't be immediately removed. This can mean waiting very late into the game before playing her, when all other removal has been used on your smaller threats and the board state is favourable to play her. If not Ysera can snowball out of control and win a game almost single handedly. 

In control matchups it's also very important to make good use of Lightbomb, preferably removing more than one of your opponents large threats, but it is often unlikely that skilled control players will overextend into the board out of fear of this card. 

Substitutions

A lot of are asking how to replace certain cards from the list, or if certain changes are a good idea, so I thought I'd write my thoughts here.

Possible cards to remove:

• Blackwing Technician - I run this card purely for the synergy with Brann Bronzebeard, as well as it's strong early game presence against common minions such as Piloted Shredder. However, if you find the dragon synergies of this card to be too inconsistent, Dark Cultist or even Eydis Darkbane and Fjola Lightbane can be used effectively in it's place.
• Velen's Chosen - This card can be substituted out for any of the 3 drops listed as substitutions for Blackwing Technician if you're looking for a slightly more consistent early game. I intend on testing out replacing 1 (or both, perhaps) copy of Velen's Chosen for Museum Curator
• Holy Nova or Lightbomb - If you find yourself playing against much less aggressive decks, the large suite of AoE removal in this deck may not be completely necessary. You could remove either one of Holy Nova or Lightbomb for a high impact card such as Vol'jin (if you're careful with Brann), Sylvanas Windrunner or even Dr. Boom if you're happy to add a Big Game Hunter to the deck. In order to keep up the dragon count in the deck, Dragonkin Sorcerer can also be a strong addition to the deck with the various buffing spells.
• Cabal Shadow Priest - Although I believe this card is undeniable strong enough to run in this deck, as an epic there are may players without access to this card. Any of the replacements for Holy Nova/Lightbomb will be fine replacements for Cabals. If you are only running one Cabal Shadow Priest then I believe Shrinkmeister to still warrant a slot in the deck, but if you are running no Cabal Shadow Priest then Shrinkmeister should be replaced with one of the possible replacements for Blackwing Technician (although Museum Curator will be an ideal substitution for Shrinkmeister when it is available). 
• Ysera and/or Chillmaw - Although I believe that it will be hard to replace these cards without hurting the strength of this deck, in order to keep the dragon count up I would recommend replacing them with Chromaggus and/or Nefarian. It's worth noting that while Nefarian seems like a strong choice due to the synergy with Brann, I feel that Nefarian is in fact a worse replacement than Chromaggus as due to the high cost it is very unlikely that you will be able to combo Nefarian with Brann Bronzebeard, and having 8 damage makes it as the only Big Game Hunter target in the deck, greatly reducing it's effectiveness. If you feel that having less dragons won't hurt the consistency of the deck too much, then Dr. Boom can also be a strong replacement. 

Update 11/12/2015

I've made some changes due to the availability of new cards to address some flaws in the deck:

• -1 Lightbomb, +1 Entomb
  Prior to release, I thought entomb would be too slow in a deck like this. But after testing, running one copy of the card is insanely strong. Often a Lightbomb would just be used primarily to remove a single minion such as Mysterious Challenger or Dr. Boom, and obviously Entomb is much better suited for this purpose. This card also greatly improved the control matchup, giving a better chance against decks such as Control Warrior which were previously hugely unfavoured; as you can not remove one of their threats while gaining a new threat of your own.
• -1 Shrinkmeister, -1 Blackwing Technician, +2 Museum Curator
  
  The main criticism that has been made against this deck is that the early game is too inconsistent, and that was absolutely true, and has always been an inherent problem with dragon priest. All decks have games when you simply don't draw any of your early minions in the starting turns, but the added requirement of these minions requiring dragons made these inconsistent starts more common with this decklist. This is why many players have taken to running Zombie Chow, but I don't think that adding even more 1 drops is the answer.
  
  Museum Curator is absolutely awesome. He's a minion that can be played on turn 1 or 2 without requiring a dragon in hand, that will often discover a minion that will help fill out your early curve even more. In the early game, due to the prioritising of class cards, there are very good odds of discovering a Dark Cultist to drop on turn 3, or another good 2 or 3 mana deathrattle card (Deathlord, Harvest Golem, etc). Increasing the odds that you'll curve out nicely in the early game will help a lot when playing against more aggressive decks, but this discover effect is also strong against control decks as it will often allow you to gain more lategame threats that the deck is lacking when playing against control warrior or control priest decks. The discover effect being a battlecry also gives another very strong interaction with Brann Bronzebeard.  Museum Curator having a non-threatening 1-2 body also means it may often survive a turn and become a great Velen's Chosen target on turn 3. 
  
  I'm removing Shrinkmeister from the deck as I find that it is not necessary in order to make good use of Cabal Shadow Priest and often ends up sitting in my hand for most of the game and then being played simply as a 3-2 body. There are a huge amount of strong 2 attack minions in the meta right now so comboing Cabal Shadow Priest is often not necessary and the slot in the deck can be better used by a Museum Curator
  
  I'm aware that removing a Blackwing Technician is a questionable decision, but with Brann Bronzebeard, Velen's Chosen and one Blackwing Technician you will seldom have no play to make on turn 3. Especially with the ability of Museum Curator to generate Dark Cultist and other similarly costed cards. You may try remove one Velen's Chosen instead of one Blackwing Technician but I believe this to be a slightly worse choice.