Yeah, the amount of times in ladder how were I've had games turn against me with C'thun and Doomcaller is pretty ridiculous. Other than having the odd lucky games with warlock, I think the main way to go against C'thun decks are priest now since Entomb is so strong and with the lack of 4-attack C'thun cards (other than Blade of C'thun, but by that time it's so late into the game at 9 mana).
I'll have a look into that dragon priest deck later on, it'd be nice to have some fun when playing against C'thun now since ladder feels so stale to me.