Hearthpwn

From Rank 5 it will always take you however long it takes to win 25 more games than you lose.  So win-rate and speed of games are really the only variables to consider.

I think Odd Rogue is a good choice post-nerf.  Take the standard list and replace Blood Knight with some combination of Blink Fox, King Mukla, and Edwin VanCleef.   Replace Giggling Inventor with some combination of Captain Greenskin, Cobalt Scalebane, and Zilliax.

4 times out of 5 the Cubelock mirror is a fatigue/value match so not having N'Zoth likely means you'll lose.  You might tech something like Ooze and Spellbreakers to increase your odds on the pressure plan, but once the game becomes a Voidlord stalemate, you will run into trouble.  Alternatively, you might try Twisting Nether to deal with their N'Zoth and hope to clean up their 1/3's the next turn, but this is inefficient and generally the best response to a N'Zoth is one of your own.

Other Cubelock mirror advice:

1. Giants are so-so in the current meta and I wouldn't run in my Cubelock, but without N'Zoth they will help with the pressure plan in the mirror.
2. Mulligan for Gul'Dan, Lackey, Giants, and Skull (keep demons if you get the Skull).  I see alot of people keeping the one drops for tempo and I think this is wrong.
3. Generally you want to Cube your Voidlords rather than Doomguards since the game will likely go late and Doomguards, like Giants, are pretty lackluster once the opponent's Voidlords come out.  Without N'Zoth though, you'll ideally Cube the Doomguards for pressure.
4. Save your Dark Pacts for Cubes rather than Lackey since the last thing you want is your opponent copying your Cube.
5. Past turns 2-4, be very conservative with Lifetap.  Using my made up statistics, about 50% of my opponents in the mirror do not understand the matchup and tap themselves 4+ cards ahead in fatigue meaning all I need to do is stall using Voidlords and collect the free win.  Without N'Zoth however, it may be correct to aggressively tap to look for the cards you need to close the game out.

With 2 Southsea Deckhands and 2 Cold Bloods, you gotta find room for a Faceless Manipulator. 

I run a list you might like.  I find this list too greedy to be consistent.  I do forgo [card]Northshire Cleric[/card] which more often than not draws zero for Museum Curator which is guaranteed a card with synergy that can help fill out your curve.

Remove: 2X [card]Northshire Cleric[/card], 2X Shifting Shade, [card]Excavated Evil[/card], Ysera, Deathwing, Dragonlord

Add: 2X Museum Curator, [card]Brann Bronzebeard[/card], Holy Nova, 2X Entomb, [card]Justicar Trueheart[/card]

Thanks for posting the deck.

The late game is what's interesting.  You can't play Golden Monkey until you C'thun, but since your absolute best C'thun is 16/16 he probably won't win you the game alone.  Since you have nothing threatening until C'thun, he is sure to get removed immediately meaning you need a pretty quick Golden Monkey follow up with good RNG to win.  In other words, if C'thun is near the bottom of your deck, I don't see how you win.

Other interesting choices besides Elise are Deathwing which only needs to be played after C'thun if he's in your hand and Alexstrasza which has the drawback of being best played before C'thun but is probably the best turn 9-10 combo in the game.  In the end I think your best bet is replacing Elise with immediate threats like Ragnaros or Grommash since they require answers no matter where they are played in relation to C'thun giving one or the other a better chance to finish.

I'm also liking Brann Bronzebeard in C'thun decks.  Worst effect is a +4/+4 C'thun buff which activates your Emperor and Shieldbearers and best effect is auto-win.  I'd probably remove a Twilight Elder or a Revenge for him.