I am currently ranking and having lots of fun with this deck.
N'Zoth the Corruptor
Revive the board of Strong deathrattle minions to seal the game (or save your ass with a taunt) The board you plan to revive will win you the game as it cannot be cleared without spawning extra Thaddius copies or jade golems.
Incredibly flexible card that can be used on many minions depending on the situations.
Most of the time you will want to save one for Feugen or Stalagg, to prevent it from being polymorphed or silenced. It is especially strong when played on turn 7 or earlier (Far Sight and Muckmorpher allow you this)
Also very strong when used on Kel' Thuzad (One will revive the other making it challenging to clear them, this will almost always grant you one KT to stay on board an generate value and constant threat)
This card is amazing for the synergy it provides in this deck.
It allows you to get one of your insane minions on board even if you dont draw them, being baits for hard removal or directly impact the game drastically. Early Aya/Sylvanas/Kel Thuzad is very troublesome to face, You can fish for Feugen or Stalagg in case you are not drawing them. Deathrattle summons count as well for N'Zoth later.
The only useless outcome is N'Zoth, but you have to be really unlucky. You can keep N'Zoth in the mulligan in control match-ups if you are scared of this.
Jade Claws Jade Lightning and Aya Blackpaw allow you to have a decent early and mid game, also tricking your opponent in thinking you are running a Jade deck. You can actually go Jade Shaman in some games, when your Muckmorphers decide to fanboy for Aya and you cast reincarnate on her or them. N'Zoth will revive a fat board of Ayas.
Feugen and Stalagg
If they were not so clunky tempo wise and to draw, they would constantly define the meta around them. Luckily it is not like that, so almost nobody expects to fight Thaddius. Especially at low ranks, people can be oblivious of their effect as they come from a loooooong time ago. Some new wild players can actually freak out when they realise what is your gameplan (usually when you reincarnate one and spawn the first Thaddius,)
One guy panicked so much he missed lethal casting double Kill Command on it.
They are the main win condition in this deck on par with N'Zoth.
Other card choices:
Hallazeal the Ascended
This guy is so cool and underrated. This is a control deck and requires healing, no doubts on it. Hallazeal can be used in different ways. You can heal with small spells (Lightning bolt, Jade Lightning Maelstrom Portal) or you can use it to reset the board and go back at full HP with Hagatha's Scheme or Elemental Destruction It is also a good bait for removals if you need it.
Nerfed, hall of famed. Even if she can be very slow, her effect can still change the game now. Pair it with Reincarnate and you have a 8 Mana Mind Control on some occasions.
The funny thing is that even if she gets polymorphed you do not really care in this deck.
Also, very very strong Muckmorpher target.
One of the coolest card ever printed, always hard to get to work properly, as he gets cleared with every possible mean on sight from your opponent. This is probably the best deck he can work in thanks to Reincarnate and Muckmorphers. Sometimes Morpher into KT into Reincarnate on turn 7 is enough to make the opponent concede.
Best case scenario? T3 Far Sight on Muckmorpher, T4 Morph Kel Thuzad into Reincarnate.
This dude is so weird the opponent is really confused on how to deal with it. The Storm Guardian CAN become a win condition. Especially against aggro. He is fitting the role of taunt generator for the turn you will play N'Zoth to prevent direct damage to the face.
If you don't have him, I would try to see if Sludge Belcher is effective as much.
It is more defensive and less strategical.
This deck severly needs card draw. This provides it with the benefit of occasional game winning discounts. I really like it.