Hearthpwn

This is my H-Sapphiron downing Warrior deck.

The idea is very simple: exhaust his supply of Minions using direct damage (Charge minions, spells, and weapons), then slowly wear him down with weapon attacks to the face. The playstyle is Control, and the key is not to allow Sapphiron to build up a large number of minions.

At 1-2 mana, H-Sapph plays Zombie Chow, Loot Hoarders, Faerie Dragons. Cleave is your friend here, so is Fiery War Axe and Heroic Strike.

At 3 mana, he gains Shade of Naxxramas, Skeletal Smith, and Dancing Swords. Cleave remains amazing against Shade. You'll ideally want a Wolfrider to take care of the skeletons, as they destroy your weapons. Do NOT be tempted into mortal striking Dancing Swords - you need those for Necroknights. Instead use a Heroic Strike if you've got one, or a Death's Bite, or a combo such as Slam + Cleave.

At 4 mana the Necroknight appears. THIS IS THE BEST MINION IN YOUR DECK! Every time I've won, i'ts been because I was able to manipulate Necroknights to take out extra enemy minions. Always save Mortal Strikes for necroknights as it's a guaranteed 2-for-1 trade.

At 5 mana the all-important Spectral Knight comes out. These are by far the toughest creature for you to take out. If there is an adjacent Necroknight, Mortal Strike it for the win. If not, there is no truly efficient technique to kill them. You must trade 2-for-1 with multiple charge cards, or use a Gorehowl or Arcanite Reaper + Upgrade.

Also at 5 mana you may see Azure Drakes. These are annoying but at 4/4 easily dealt with for their cost.

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Attack Selection

You should almost never use Charge Minions against Sapphiron's face. Assuming you use both Upgrades on different Arcanite Reapers, your maximum possible face damage is 12 (Fiery Axes) + 16 (Death Bites) + 36 (Upgraded Reapers) + 7 (Gorehowl) = 71 face damage. You can use 26 weapon damage against minions (about as much as your HP pool can sustain) and still have 45 left to take Sapphy down. Charge minions, while frequently card-inefficient, are your best hope of taking down tough minions like spectral knights.

The only time your minions should Charge Sapphy's face is when he is close to kill range. If your Wolfrider + Murloc can provide the last 5 damage to finish him off (or bring him to lethal next round) then you can safely use up your remaining Chargers.