Mulligans
General Mulligans
generally you want to have cards that offer you c'thun buffs on early stages so by turn 7 you can guarantee 10 armor gained by shieldbearers. acolyte of pain is good since it lets you draw more = play your combo earlier. fiery war axe is a solid value card which allows you to remove early game threats.
Aggro Mulligans
against aggro decks you want to mulligan cards that are good for fighting early ways of aggro. also if your enemy is possibly playing deck centered on flooding board revenge is extremely nice. brawl might be a little bit slow, but it allows you to buy some turns till you can stack armor through shieldbearers or shield blocks. crazed worshipper is yet enother interesting card. since silence is being nerfed, most of decks will not run owls, which makes a 6 health taunt pretty solid. + it buffs your old god which is good. the one thing you have to remember well is that most aggro decks don't have big removals like bgh, death, execute ect which allows youto play your old god as soon as you can, as C'thun itself is a wincondotion and sets aggro decks on timer.
Midrange Mulligans
against midrange decks you want to mulligan cards which let you fight for board or clear efficiently enemy minions. beckoner of evil and disciple of c'thun are good minions, that not only help you earlygame, but also buff your c'thun.
Combo Mulligans
against combo decks you want to draw as much as you can and play c'thun buffers as fast as possible. since minions combo deck's play are not rly threatening, concentrate on your combo and you total health (to stay out of their combo range eg. more then 22 health against old murloc OTK, although murk eye is out of standard, so have no fear. you should mostly fear c'thun decks as combo based. if you have enough total hp you should be fine + most c'thun decks are control oriented).
Control Mulligans
against slow control decks you want your worshippers and card draw. acolyte is pretty solid against some classes. fiery war axe is great as an early removal. execute is a way to remove some beefy minion if it somehow is on the board. (do not mulligan execute if you have no way to deal damage to enemy minion.
my first try on c’thun warrior. it’s based on control warrior + c’thun combo. i realise this deck requires more drawing, but it seems to me that the list is at least decent and can be solidified and then perfected so that it will be cinsistent enough. the otk in deck is absurd. enabling 2 ticks of thaurissan with blood warriors gives player a possibility to deal 60 dmg (brann + cthun + charge). in case you did not fully buff your c’thun and had him die, youcan bring him back via doomcaller. basically allows youto have a boardclear + huge threat as soon as you draw the old god. the main problem this deck has is consistency. it seems that the deck requires more cycling, although i’m not sure what to cut. the combo in this deck is made to easily deal with control heavy decks even fatigue style warriors (since they are rarely going to get 30+ armor, since you have some minions who can be enough of threats). against agressive and midrange decks playing you c’thun alone should be enough to close out a game, or let you drag game to late stages when you can resummon c’thun and close up the game.