Template:Vaelastrasz the Corrupt strategy
Normal mode
Vaelastrasz's Normal mode hero power Essence of the Red forces each player to draw two cards. He uses this to his advantage by milling both your cards and his own to use cards like 
Goblin Sapper, 
Twilight Drake, 
Volcanic Drake, Molten Giant and Clockwork Giant, in which the cards in both hands and the number of minions died that turn matter. On top of that, he uses Naturalize to cause you to reach fatigue and Gang Up to re-stock his deck to prevent himself from reaching fatigue. He also combos with his spells to attempt to remove your smaller minions and at the same time create some small minions to stall till both hands are full.
A good class against this is warlock with low cost/effective Deathrattle minions from Naxxramas, minions and spells with discard effects. You will also need Taunt minions and powerful spell cards such as Hellfire, Shadow Bolt, Corruption, Sacrificial Pact and Soulfire. Primarily, you want to focus on the Demon type to synergize with your spells. DO NOT include any card draw mechanisms else you will fatigue.
Rogue is also a very good class against Vaelastrasz. Gang Up can be used against him on his Clockwork Giant and your Preparation, Backstab, Sap, Assassinate and Vanish are more efficient than his. If you have Mountain Giants of your own, all the better.
Heroic mode
Beatable using mage, use a deck with low-cost spells. Key cards are Sorcerer's Apprentice, Mirror Image, Flamewaker and 0-mana cost minions.
Generally you want to play Mana Wyrm or Leper Gnome on turn 1, and Sorcerer's Apprentice + Mirror Image + Arcane Missiles or 0-mana minion on turn 2. Then depending on the situation, try to keep Sorcerer's Apprentices and Flamewakers alive (if possible) and go for the face. Using this strategy, the boss is not able to utilize his desired tactic well and you should be able to overpower him. Fireball + fatigue damage (great if his full hand forces him to discard Gang Up) are usually enough to finish him. Use Frost Novas after you lose your Taunts to prevent him from hitting your hero.
Another class that deals with Vaelastrasz very well is hunter. A fleet of low cost minions (0-2 mana) ensure pressure and damage. Explosive Trap and Hunter's Mark are cheap ways to clear Vaelastrasz's board, and Unleash the Hounds can deal lots of damage in short time.
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