Hearthpwn

Overview:
Abuse the portals and freeze to limit his damage.

Mulligan:
Mulligan for Ice Lance or Glacial Shard and a cheap taunt: Dirty Rat, Mirror Image, Shieldbearer, Annoy-o-Tron.

Early Game:
Turn 1, play Ice Lance or Glacial Shard, so you don't take 16 damage straight away. From there, make sure you always have a taunt on the right, and at least 1 minion on the left. This way you keep from taking massive damage. He will also seem to focus on the Windfury minion with his removal.

Arcane Nullifier X-21, Dirty Rat and Deathlord are all MVPs because of elusive and the fact that Netherspite has no minions in his deck.

Mid Game:
Continue to block the portals, and freeze him whenever you can. He will do everything he can to remove the Snowchugger, Water Elemental and Glacial Shard.

Late Game:
On turns 9 and 10 expect back to back Twisting Nethers. Both of your HP will likely be very low, keep blocking the portals and hitting face, closing out with Fireball.

My Other One Night in Karazhan Decks:
The Parlor
     Silverware Golem (Patron Warrior)
     Magic Mirror (Silence Priest)
     Chess (White King)

The Opera
     Romulo & Julianne (Taunt Warrior)
     Big Bad Wolf (Resurrect Dragon Priest)
     The Crone (Murloc Shaman)

The Menagerie
     The Curator (Exodia Mage)
     Nightbane (Resurrect Priest)
     Terestian Illhoof (Thief Priest)

The Spire
     Shade of Aran (Aggro Mage)
     Netherspite (Freeze Mage)
     Free Medivh! - Prince Malchezzar (Jade Taunt Druid)