-vs Control = Twilight Drake, all demons if you have Bloodreaver Gul'dan in starting hand, i not then Voidwalker only.
-vs Aggro = Mistress of Mixtures, Mortal Coil, Voidwalker, Defile, Doomsayer and Drain Soul if against Hunter.
-vs Jade Druid = Just try to gain cards to good curve.
- Possible to remove = Bloodmage Thalnos, 2x Doomsayer, 1x Hellfire, 1x Siphon Soul, The Lich King and Twisting Nether.
- Cheap replacements = Golakka Crawler, Dread Infernal, 1x Shadowflame, 1x Shadowbolt, Bog Creeper, Bonemare, Defender of Argus, Tar Creeper.
- More expensive replacements = 1x Kabal Trafficker, Mountain Giant (pretty good against Jade Druids), 1x Primordial Drake, The Black Knight but I don't recommend using him right now, Elise the Trailblazer, Faceless Shambler (if playing with 2x Mountain Giant).
- Don't worry about using Hero Power against aggro, but use it wisely.
- Play more as a Tempo deck against aggro decks or Jade Druid.
- Remember that hunter likes to buff beasts, so don't wait for perfect Defile, just control the board as much as you can and try to have more tempo. Twilight Drake can really help, even as a 4/5.
- Against control matchups, Bloodreaver Gul'dan is your win condition. Don't hesitate to play him when you have time for it, even if he doesn't summon any demons.
- It's ok for you to take damage, but play around cards that opponent's deck can go from hand to face, like Arcanite Reaper or Fireball.
Edit: Forgot the proof :P Here you go:
Hope you'll hit the legend with this one, good luck :)