I found my best matchups to be against other Control Warriors, Zoo, and most Priest/Mage archetypes. I performed quite decently against Paladin, Midrange Shaman, Tempo Warrior, and Midrange Hunter, went even against Miracle Rogue, and fared quite poorly against Aggro Shaman, Aggro Warrior, and Ramp Druid. I think the Control C'thun archetype is quite powerful and a lot of fun. The final decklist isn't particularly innovative, and was in fact largely based on
Novalicious' List on HearthPwn. What I have to offer in terms of discussion are the various adjustments I have made in terms of card choices and deck style, as I experimented with a great variety of cards and subtypes as I climbed, as well as some insight into the matchups that I made these adjustments to address.
Initially, I was running a deck largely resembling
Sjow's early season list which notably includes Blood to Ichor, Slam, Brann Bronzebeard, and Beckoner of Evil, all of which I have excluded from my final list. I initially went 5-16 with this version, dropping from my rank 14 starting point to rank 15/16 (largely due to my initial ineptitude) before I decided to cut all three of those cards, 1 Acolyte, and Elise Starseeker for
a much greedier package that included 2x Doomsayer, Harrison Jones, Skeram Cultist, Sylvanas, Baron Geddon, and Ysera. This deck and subsequent revisions netted me a
~73% winrate (78-29) from rank 15 to legend.