I have played hearthstone since the beta and honestly I have never felt like a deck is as invincible as this. Seeing how overpowered Razakus priest is in standard I was curious how it would perform if you put Reno Jackson and Lightbomb in it. I went 30-1 on my way to rank 3 and I will continue to play the deck hopefully up to legend tomorrow.
The pirate matchup is quite frequent and the only one I've lost to so far. You will need to mulligan for the early board clears (Potion of Madness, Doomsayer, Spirit Lash, SW: Pain and SW: Horror). Out of minions the only ones I tend to keep are Kazakus and Reno Jackson.
Against jade druids I mulligan for Kazakus, Raza and Shadowreaper Anduin. The sooner you get the 0 mana deal 2 hero power going the better. You should try to cycle as hard as possible. If you draw a doomsayer try to play it after a full board clear. The silence typically goes towards Aya. I have on occasion played Reno just for tempo as jade druids don't really deal much damage until the late game and by then they deal 55-1000 damage per turn, so the heal doesn't really help. I have finished off many games with a combo of hero power - Velen - HP - Radiant Elemental - HP - Mind Blast - HP - Smite - HP.
Other than those two decks there hasn't really been any consistant opponents. Against aggro you should look towards the Pirate Warrior approach and against control the Jade Druid approach works rather well often.
Below are my reasons for picking each card and how important I feel like they are.
Silence - Essential. Can always be fit into a turn due to the 0 mana cost. You can play it to silence a threat and when there's none just keep it for a combo with the hero power in late game.
Holy Smite - Essential. Most commonly used as part of an OTK combo, can help clear some early game minions against aggro.
Northshire Cleric - Essential. Huge draw engine.
Pint-Size Potion - Essential. Combines well with SW: Horror and Potion of Madness.
Power Word: Shield - Essential.
Bloodmage Thalnos - Important. Helps improve your aoe spells, most importantly Spirit Lash. Tainted Zealot might make a reasonable budget replacement.
Doomsayer - Essential. Stops early game against aggro decks and combines well with board clears against control.
Loot Hoarder - Important. Adds cycle and combines well with the 0 mana hero power.
Mind Blast - Essential. Adds 14 damage in combination with Prophet Velen.
Novice Engineer - Important. Adds cycle and combines well with the 0 mana hero power.
Radiant Elemental - Essential. Can be played early against aggro or kept in the hand for a greater OTK combo near the end of a match against control decks.
Shadow Visions - Essential. Don't keep it in the early game, use it to find spells you need mid- or late game.
Shadow Word: Pain - Essential. Important against aggro and often gets high value vs control decks.
Spirit Lash - Essential. This new spell helps with board clears and heals you at the same time.
Acolyte of Pain - Essential. Adds cycle, often combined with Spirit Lash or Lightbomb.
Kabal Courier - Not so important. Was mainly curious about how this card would perform. Could be replaced for an Ooze if you are facing a lot of pirates.
Shadow Word: Death - Essential. Very good against control decks.
Kazakus - Essential. No budget cards directly replace this, but you could fit in a Tar Creeper, Ooze or Gnomish Inventor if you don't have it.
Priest of the Feast - Essential. Simply amazing against aggro. Often aids in healing after you go Anduin mode.
Shadow Word: Horror - Essential. Good against aggro, often combined with Pint-Size Potion against control decks.
Azure Drake - Essential. Adds cycle and spellpower. Does not die to Dragonfire Potion.
Holy Nova - Important. Combines well with Thalnos or Azure Drake. Can often be used on turn 5 to set up Dragonfire Potion or Lightbomb.
Lyra the Sunshard - Important. Helps fill up your hand if you draw a bunch of spells and little cycle. Used often as just a 3/5. If you don't have it you could replace it with Curious Glimmerroot, Gnomish Inventor, Emperor Thaurissan or other cards you want to try teching in.
Raza the Chained - Essential. Makes the entire deck along with Shadowreaper Anduin.
Dragonfire Potion - Essential. Huge board clear and often fits perfectly with your opponents turn 6 boards.
Lightbomb - Essential. Same as Dragonfire Potion, slightly stronger lategame though.
Reno Jackson - Essential. Because he wins matches when you draw him against pirate players.
Prophet Velen - Essential. Huge part of the OTK potential in the deck. Against aggro or midrange you can often just play him on turn 7, just be mindful that Shadowreaper Anduin also kills your own minions.
Shadowreaper Anduin - Essential. The bread and butter of the deck. You won't always need his ability to kill several big minions. I often drop this guy just for tempo on empty boards and sometimes even if it kills my own Raza.