Hearthpwn

I have been using this mech priest deck to climb the ranks for the last few season. 

This deck out tempos most midrange/control decks and holds its own versus most aggro/tempo decks.

Play Testing Statistics:

People have asked for proof on how well this deck preforms so I played 30 ranked games ). 17 with the original deck list and 13 with the new one. (I have no idea on where to get a win/loss tracker so I just used pen and paper.)

I have not reach Legend with this deck due to lack of time and not wanting to grind ladder. I am sure legend can be reached with the deck as you only need a 51% win ratio to do that.
If I do find time, I will try to reach Legend, but until then I leave it for you people to try.

Please keep in mind that this is only 30 games of recorded testing, I have done more than that, but have not recorded the games. Don't take the win rates against some classes for granted. Do some testing by yourself to get a feel of the deck's good and bad match-ups.

Druid: 0 Played

Hunter: 4 Played - 3 Wins - 75% Win ratio
Wins- 2 Face - 1 Control  
Losses- 1 Midrange

Mage: 8 Played - 6 Wins - 75% Win ratio 
Wins: 3 Mech - 1 Freeze - 2 Tempo
Losses: 1 Mech - 1 Tempo 

Paladin : 1 Played - 1 Win - 100% Win ratio
Wins: 1 Dragon

Priest: 3 Played - 3 Wins - 100% Win  ratio 
Wins: 1 Control - 1 Dragon - 1 Combo

Rogue: 3 Played - 2 Wins - 66% Win ratio
Wins: 2 Oil
Losses: 1 Tempo

Shaman: 1 Played - 1 Win - 100% Win ratio
Wins: 1 Mech

Warlock: 8 Played - 3 Wins - 38% Win ratio
Wins: 2 Zoo - 1 Handlock
Losses: 1 Zoo - 3 Demon Zoo (Midrange Warlock) - 1 MalyLock
(This is misleading as the deck preforms well against the zoo and the zoo part of Demon Zoo. Losses are do to Voidcaller pulling cards like Mal' Ganis and Doomguard in the early game and not having adequate removal for the pulls. A silence of any form may need to be added to the deck.)

Warrior:  2 Played - 1 Win - 50% Win ratio
Wins: 1 Patron
Losses: 1 Control

Total Win Ratio: 66%

Playstyle:

If you have ever played Midrange Paladin and Control Priest, then you should have a a good idea on how this deck works.

If, not then think of Mech Mage where you play more control-like while still trying to gain tempo. (Make sure not to over extend.)

In essence, this is like Midrange Priest that is more geared towards control.  The mech aspect is used to gain much needed tempo in order to compete with the meta. 

This deck may or may not have a large learning curve depending on what kind of player you are.

Mulligans:

Aim for a decent curve. (1,2,3 or possibly 2,3,3) 

If you have Mechwarper consider keeping Mechanical Yeti or Piloted Shredder. (Also consider keeping Upgraded Repair Bot if you think Mechwarper will survive until turn 4.)
Only keep Tinkertown Technician if you have a early game mech or if you want to coin it out for Velen's Chosen. (Spider Tank is far better for this.
Velen's Chosen should only be kept if you have a 1-2 mana minion or will coin out a 3 mana minion.

Even though keeping Holy Nova may seem like a good idea against aggro/tempo, it usually is not. At 5 mana, Holy Nova is too slow to be kept against aggro/tempo. It is better to try to control the board with minions than rely on 1 spell. Keep Shadow Word: Pain instead ofHoly Nova.

Match-ups:

Disclaimer: This match-up guide assumes that you know how to play against certain meta decks and use common sense. This is a very basic match-up guide and you will need to learn how to play with this deck on your own. The deck requires a certain "play style" (If you can call it that) that is not easy to explain in words, however the "play style" can be learned easily through play.

Druid:

Druid is fairly easy.
Try to gain as much tempo as you can in the early game and make sure you have answers for his minions. (It if worth keeping Shadow Word: Death in the opening hand.)
Remember to keep out of Force of Nature + Savage Roar range.
Spread out your buffs so you don't lose a large minion to Keeper of the Grove.

Hunter:

Hunter is by far the most difficult match-up. 
Make sure that you know what kind of deck it is. (ie. Face, Mid-Face, or midrange.)
Face hunter is extremely difficult, however you can still win. Control the board as much as you can and only heal yourself. Try to keep a strong board and hope the opponent doesn't draw the exact cards for lethal.
Midrange hunter is a tossup. Again, control the board as much as you can, but also push as much damage as possible. Be careful of Freezing Traps and spread out your buffs as a result.
Mid-face is easier than face hunter, but more difficult than midrange. Play like you would against face hunter, but you can heal your minions. Force the opponent to make trades while you exert damage. Same as midrange, be careful of Freezing Trap and make sure to have an answer to Savanna Highmane.
If you don't know what the opponent's deck is, then assume mid-face as the play style of mid-face encompasses the play style of midrange and face hunter. (The match-up improves if you know what the deck is and play accordingly.)

Mage:

Most of the time is mage is easy.
Mech mage is a walk in the park if you can control the board well enough. Make sure to remove Mechwarper.
Tempo mage is more difficult. Control the board as much as you can and push as much damage as possible. Force the opponent to make unfavorable trades and waste removal/burn on unimportant minions.
Control mage is not something I have played  against much, so I can offer no advice.
Freeze mage will be covered later.

Paladin:

Against midrange/control, control the board and make the opponent waste removal before you bring out Ragnaros the Firelord and Troggzor the Earthinator.
This matchup is strange because it can either way depending or both of your draws. Most of the time it is in your favor.
Against aggrodin, play much like you would agaisnt face hunter. (This is 10 times easier than face hunter, but can still be difficult.)

Priest:

There really isn't much to say here.
Control priest is really easy if you don't play into board wipes and play against aggro priest as you would against face hunter. (Most mech priest are more aggressive than this deck so play against them as you would against an aggressive midrange deck.)

Rouge:

Oil rouge and Malygos rouge will be covered later.
Play against mech rouge and tempo rouge (if that is still a thing) as you would against mech mage/tempo mage.

Shaman:

Shaman require no certain play style. Just control the board and that should be good enough.
Play against mech shaman as you would against mech mage.
Malygos shaman will be covered later.

Warlock:

Against zoo control the board and try to never let the opponent snowball. This is one of the only mat-ups where you can flood the board with little consequences. This is quite difficult if you get a bad hand and bad draws.
Handlock is pretty much a lost cause. This deck does not have the tool necessary to deal handlock's threats. The match-up can still be won, but it is unlikely. My only tip is to not play into Shadowflame.
I have no tips for Demonlock as the decks vary vastly. It could be more like handlock or more like zoo. Play against it like you would against the deck it resembles.

Warrior:

Patron warrior is the only deck that I will not be covering in the "Combo deck" section as it is a very easy game. Make the opponent waste removal on early minions that are buffed mildly. Save Holy Nova for an opportune moment or with Velen's Chosen. Shadow Madness can be used to get lots of Grim Patrons for you if played at the right time. Remember not to flood the board because of Frothing Berserkers + Whirlwind effects. Also try to keep above 12 health as some decks run Grommash Hellscream.
Control warrior is very hard as this deck can't deal with too many large threats. The 4 main things to keep in mind is to control the board as best as you can, make the opponent waste removal, don't play into Brawl and hope the opponent doesn't draw well. If the opponent plays Grommash Hellscream, doesn't kill you, and you can remove Gromm, the matchup because a lot easier.

Combo Decks:

This category include Freeze Mage, Oil Rouge, and Malygos Rouge/Shaman/Warlock.

These match-ups are difficult due to the amount of burst that these decks have.
Make the opponent waste burn for removal (ie. Blade Flurry, Fireball, Darkbomb), stay above the amount that they can burst you down, don't play into board wipes, and try to kill them quickly or stall until their burst is gone.

Substitutions:

Troggzor the Earthinator / Ragnaros the Firelord can be substituted with Dr. Boom, Sylvanas Windrunner, Sludge Belcher (use Arcane Nullifier X-21s if no Naxxramas), Holy Nova, or Force-Tank MAX. (Mind Control may also work.)

If one or no Cabal Shadow Priest are owned, remove the Shrinkmeisters. Replace these with Sylvanas Windrunner, Sludge Belcher (use Arcane Nullifier X-21s if no Naxxramas), Cogmaster, or Annoy-o-Tron. (Auchenai Soulpriest + Circle of Healing may also work.)

If you do not have Naxxramas, Loatheb can be substituted with Sylvanas Windrunner, Defender of Argus, Holy Nova, or Arcane Nullifier X-21.  (Thoughtsteal may also work.) 

 

Reformatting against the meta: 

If you find there is too much aggro, consider removing the Shrinkmeisters and 1 Mechanical Yeti to add a second Holy Nova and Annoy-o-Trons. (Also consider adding Sludge Belchers / Arcane Nullifier X-21s.)

If you find there is too much control, consider removing 1 Mechanical Yeti, Shadow Madness and Shadow Word: Pain to add Sylvanas Windrunner,  1 Thoughtsteal, and 1 Lightbomb (If you do not like Lightbomb use a second Thoughtsteal or a Mind Control.)

Reasons for Troggzor the Earthinator over Dr. Boom

I know this choice seems strange, but bear with me.

• Against control, the opponent will have most likely burned removal on the mechs leaving you with a non-removed Troggzor the Earthinator on the board.
• Against aggro, you can control the board really well given a semi-decent starting hand and semi-decent draws. After minions have been removed, the opponent will most likely need to use spells to remove Troggzor the Earthinator (not removing Troggzor the Earthinator is a HUGE mistake that can cost them the game if you keep control of the board). Since most aggro decks run little removal, it usually leaves you with a 3/5 Burly Rockjaw Trogg that will continue to grow as the opponent tries to burst you down. If the Burly Rockjaw Trogg does get removed, then you just got a 2 for 1 while also using up 2 of the opponent's burst cards. This may not seem like a huge boost in value, but the extra health usually wins you the game.
• (This is just a little side note.) The deck does not need the late game tempo that Dr. Boom supplies. If the deck is played correctly, Dr. Boom will be a fancy War Golem, and the value from Troggzor the Earthinator will be lost.
• Feel free to experiment with Dr. Boom, but as I see it, Dr. Boom's purpose is not needed and Troggzor the Earthinator's use is something that this deck needs.

Side Notes:

• The only 1-mana minion is Northshire Cleric because I have not found any cards that can be cut for Cogmaster / Clockwork Gnome.
• No Shadow Boxers because of the above reason. Also I do not really care for the card without Circle of Healing and a second Holy Nova. Try it if you want.
• Harvest Golem is not include because of the first point.
• Removing 1 Mechanical Yeti and adding Sylvanas Windrunner may be stronger, however I can not check as I do not have Sylvanas Windrunner. (Only do this if running the original decklist.)
• This deck destroys Grim Patron Warrior for some unknown reason. (I really don't know why, but it does.)
• Getting a bad hand can make you instantly lose a game against aggro if you don't stabilize quickly. (If you do stabilize and it isn't aggro hunter, the game usually becomes a cake-walk.)
• Feel free to Improve upon this deck as you see fit, but please make sure to credit me if you use the deck. 

Suggestions and constructive criticism is encouraged.