Hearthpwn

Overview:
Use Elise Starseeker to transform your deck into all legendaries.

Mulligan:
Look for Shadow Word: Pain and Power Word: Glory. If you get Elise Starseeker, great, but this is in for the long game, and it won't be a problem.

Early Game:
Clear the minions as best you can and heal as needed. Use Shadow Word: Pain on the Fen Creeper.

Mid Game:
Power Word: Glory will really help you here, and feel free to use Excavated Evil as needed. Use Justicar Trueheart, so your hero power will outdo the damage from his hero power and Elise Starseeker when you get her. Try not to spend more card than necessary at this point, so you can maximize the legendaries.

Late Game:
Kill whatever spores remain and go face.

Video:

My other Curse of Naxxramas decks:
Arachnid Quarter
     Anub'Rekhan (Taunt Warrior)
     Grand Widow Faerlina (Odd Warrior)
     Maexxna (Dragon Priest)

Plague Quarter
     Noth the Plaguebringer (Spell Hunter)
     Heigan the Unclean (Control Shaman)
     Loatheb (Control Priest)

Military Quarter
     Instructor Razuvious (Taunt Druid)
     Gothik the Harvester (Mill Druid)
     The Four Horsemen (Resurrect Priest)

Construct Quarter
     Patchwerk (Freeze Mage)
     Grobbulus (Odd Patron Warrior)
     Gluth (Divine Shield Paladin)
     Thaddius (Control Warlock)

Frostwyrm Lair
     Sapphiron (Fatigue Mage)
     Kel'Thuzad (Mill Rogue)