Hearthpwn

This game cheats.  Either I get a bad hand, or when I get a perfect hand so does he and keeps my minions dead until he gets his second phase.  I've tried several Priest and Paladin decks.  And when I finally do get his board under control he Twisting Nethers everything.  What's a good deck?

I used Priest Inner Fire / Divine Spirit shenanigans. Beat him first attempt, although I freely admit that was due to getting the luckiest opening hand and early draw imaginable.

Evey time I've tried Inner Fire / Divine Spirit he steals it.

Don't buff a minion huge during phase 2, play a bunch of small minions.

Here are some video guides for the heroic bosses, http://www.hearthpwn.com/forums/hearthstone-general/streams-and-videos/15411-rabidwhales-naxxramas-completion-videos-heroics

AND OF COURSE as soon as I post this topic, I get the perfect game.  Perfect starting hand, perfect trades, and Kel'Thuzad doesn't use his minion stealing power until about turn 16.  He skipped it every turn even though I had about 4 really great minions on the board.

Since OP is satisfied and thread is no longer needed, I'd like to ask: Do we get heroic card back if we complete them in next season?

Yes, as far as I know you'll be able to get the card back from beating naxx on heroic whenever. 

I used a resurrection based shaman and I think I got him on the 2nd try.  Never even got to play kelthuzad vs kelthuzad :-(  Basically lots of stuff with death rattle, ancestral spirit and reincarnate.  Throw in kelthuzad and baron rivendare.  Lighting storms, earth shocks, lighting bolts, and flame tongue totems.  Pinch of luck and you're good to go.

i used warlock to beat him.. in my opinion this is the least unluck based approach.

I posted the deck a pretty good while back.. here is what i created to beat him

http://www.hearthpwn.com/decks/94332-kelthuzad-heroic-best-deck-low-cost-also

I used a paladin deck to beat him.  You can find my deck and guide here:

http://www.hearthpwn.com/decks/94043-winning-heroic-kelthuzad

you basically need to create a lot of tokens and use Illidan Stormrage in the end game.

the warlock i posted above has similar approach but dont need something as rare as illidan

After many failed attempts with other people's decks, I whipped him silly on the first try with a Secrets Paladin.  Not sure if that's a thing already, but it sure put a smile on my face!  

I just defeat him with a standar odd paladin deck, first try. 2nd phase, your health is not important, just keep control of board and fill it as much as possible.

Exodia paladin first try.

Well in the here and now times, no dice on this deck now.