Another HS post! C’Thun Rogue was the very first deck that I built when Whispers of the Old Gods released, mainly because I opened most of the cultists in the initial ~25 packs that I had gold for. It was a super greedy deck, utilizing most of the cultists, Brann, Shadowsteps, and Doomcaller for the potential to play a 20+ C’Thun multiple times throughout a game. Looking back now, it was a bad deck, but still allowed me to complete the WotOG initial quests easily because everyone else was experimenting in that unstable meta.
Nowadays outside of Druid and Warrior, C’Thun decks are largely considered to be not viable for competitive play. They are more considered to be beginner decks, as they are very cheap and easy to build since most of the cultists are common/rare and C’Thun is given away for free.
However, I do think that certain C’Thun decks are viable and certainly good enough to get Rank 5 consistently each season. The key is to not be too greedy. People quickly figured out that stuffing a C’Thun deck full of cultists gave it extremely polarizing matchups against the decks you would see on ladder. It would lose horribly to aggro because a)you would often be dead before Turn 10 and b)other than Disciple, the C’Thun cultists were slow, value oriented cards. It would also lose to Tempo decks because you would never get the board.
Clearly, the answer is to minimize the amount of C’Thun cultists. One of the main reasons to play a C’Thun deck is the 7 mana legendary Twin Emperor Vek’lor. Two 4/6 taunts for 7 mana is no joke. It is insane value if played on curve as long as you can get the battlecry off. Thus, the amount of cultists in a deck needs to be just enough to consistently get the Twin Emperor battlecry, but not too much that it bogs down the deck. In my experience, that amounts to about 4-5 cultists. Thus, the most successful C’Thun decks are hybrids or modified versions of existing decks. C’Thun Warrior is just Control Warrior with certain of the classic key cards replaced(like Ancient Shieldbearer for Shieldmaiden) and C’Thun Druid is just Ramp Druid. You can also see that it is very important for C’Thun decks to have multiple win conditions. Having C’Thun be the sole win condition is terrible because there is no guarantee that you will ever draw it in a game. So your deck needs to be fully capable of winning without drawing C’Thun. He is really there as an alternate win condition or a late game bomb.
There is not as much support for C’Thun in the Rogue class compared to Druid/Warrior/Priest, but I think the Rogue variants can be just as strong. The class has some unique ways to make C’Thun more effective, like Shadowstep or using the coin from Tomb Pillager to play C’Thun earlier than Turn 10. One big issue with a lot of C’Thun decks is a lack of card draw, and it is a truly terrible feeling to have your C’Thun buffed up to a reasonable level but never end up drawing your Twin Emperors or C’Thun. Rogue can mitigate this problem since the class has so many ways to cycle using Gadgetzan Auctioneer.
Thus, I think the strongest C’Thun Rogue variant is the Miracle hybrid. The core cards are:
2 Backstab
2 Preparation
1 Bloodmage Thalnos
2 Eviscerate
2 Sap
1 Edwin VanCleef
2 Fan of Knives
1 Shadow Strike
2 SI:7 Agent
2 Tomb Pillager
2 Azure Drake
2 Gadgetzan Auctioneer
1 Twin Emperor Vek’lor
1 C’Thun
That leaves a whopping total of 7 flex spots. Of course, a good portion of these will be dedicated to C’Thun cultists. Deciding on how many and which cultists to use is pretty tough. Generally, the best ones to use are Disciple(you can almost think of him as another SI Agent) and C’Thun’s Chosen(divine shield is great and 4 attack trades with a lot of important minions).
Blade of C’Thun is a card that deserves special attention, since it is the Rogue specific C’Thun card. Its effect is super strong and allows Rogue to actually deal with big minions. Generally, the best way that Rogue can answer something like Ysera or Grommash is to temporarily get rid of them with Sap, and proceed to out tempo the opponent. So it’s never a permanent answer. There IS Assassinate, but that card is incredibly mana inefficient. Blade of C’Thun is also mana inefficient, but it does at least leave behind a 4/4 body and the C’Thun buff can be incredibly threatening. The problem is that the card is completely dead against aggro, so I think running 2 is a mistake. 1 is the sweet spot if you decide to use this card.
The other spots are pretty standard. They can be filled in with a lot of cards you would expect from a standard Miracle deck, like Earthen Ring Farseer, a 2nd Shadow Strike, Violet Teacher, or Xaril. There should also be at least one extra cheap spell for the Auctioneer synergy, like a Deadly Poison or Journey Below. Or even a Shadowstep if you want to get greedy with the C’Thun battlecry.
In my variant of the deck, I have 1 Deadly Poison, 2 Beckoner of Evil, 1 Disciple of C’Thun, 2 C’Thun’s Chosen, and 1 Blade of C’Thun. The deck plays pretty much like a standard Miracle Rogue. You can make big tempo plays and flip the board state in an instant. And C’Thun just ends up being an alternate win condition. One important difference is that the deck can actually play proactively as early as Turn 2, since there are 2 Beckoner of Evils.
Ryzen had a lot of success in the May ranked season with his version of the Miracle C’Thun hybrid deck. I’m not entirely sure why he does not run Edwin, but he was able to get Top 10 Legend, so I really can’t criticize.
Iksar, the associate game designer of Hearthstone, has an interesting version of C’Thun Rogue which runs 2 Blade of C’Thuns and no cultists!
There are also a number of Reno variants of the deck that people have found success with, and sometimes they also have both C’Thun and N’Zoth! With these decks, a big difference is that the Rogue’s card draw power suffers, and since you are running 1 ofs consistency can be an issue. But your individual card quality is much higher on average. I personally don’t find these decks to be very strong, but they are super fun. With Brann, Shadowsteps, Sylvanas, and Shadowcaster there are all sorts of shenanigans that are possible. It is not at all uncommon to play multiple Renos, C’Thuns, and N’Zoths in games with this kind of toolset.