I came up against a Rogue with a cool N'Zoth deck similar to this on ladder in wild. I tried to build my own -maybe a bit slower- version of it.
The goal of the deck is to grind out your opponent. Heal up, play taunts and then play and gang-up N'Zoth, the Corruptor to make them concede. A lot of games end up in fatigue, but in some cases people just concede beforehand. It is also possible to play this as a mill deck if you mulligan for Brann Bronzebeard and Coldlight Oracle from the start. With a Preparation/Vanish combo you can absolutely destroy opponents with big hands.
Aggro matchups just require removal, healing or taunts. So try to get Doomsayer, Betrayal, Fan of Knives, Deathlord or one of your 5-drops on the coin, if it's defensive. If it drags to mid game, you can try to Shadowstep on a Healbot until you get Vanish or taunts. Saved my ass a few times, but usually it does not get this far since they either concede by turn 8 or you die by turn 5-6.
Control matchups force you to hope they don't steal or destroy your N'Zoth. Main goal here is to use Gang Up on N'Zoth and then you're going to stroll through late game. Play around transform effects with your taunts (preferably in Valeera form) if needed and only play N'Zoth if you can Shadowstep or Gang Up the same turn. Best to mulligan for your Deathlord and Sludge Belchers so you can get your N'Zoth train going asap.
Note that when you are in Valeera mode, you can play a shadowstepped N'Zoth for 8, then use Preparation and Gang up twice to gain 6 N'Zoth (and turns). This is usually a sealed fate for your opponent. Also great after a King Togwaggle or Azari, the Devourer play.
Worst match-ups might be combo decks, since you cannot really put pressure on them. Probably best to mulligan for cheap minions and play them asap. The Darkness might also help here, but not a guarantee. The easiest might be to mulligan for Brann Bronzebeard and Coldlight Oracle/Shadowstep and try to mill them.
Alternatively, Deathlords can be very useful in disrupting minion-depend combos. If you can double those with Valeera (if the match lasts that long) you can screw up their game plan horribly. A tech card against combo might be Void Ripper, since you can use your taunt's health as attack, but I never tried since most matchups were not combo decks.
I feel this is already a very tight list. You can even beat jade druid with this in most cases, since their single token generation in late game cannot beat your constant refilling of the board with a fresh N'Zoth for more than a turn or two. In order to stall for that time I squeezed in The Darkness to make them refrain from drawing too fast and against Reno decks or the rare Raza priests. Also screws with big mage's Dragon's Fury. Though it really does not matter too much, but it's not a must.
You could exchange The Darkness for anything that costs 4 mana in that slot. Notable options are any minions targeting secrets like Eater of Secrets, Kezan Mystic, or maybe an ooze for weapon removal. I also tried versions with Barnes, Saronite Chain Gang, Prince Valanar or Spellbreaker. It's really up to the meta and your preference. Even a Dirty Rats might help against combo decks. Remember, you can play all those cards twice in Valeera mode.
If you are only facing control and deck burners, then maybe you can just put in an Academic Espionage for 20 extra cards in late game instead. I doubt the meta would ever slow down that much though :P