Mulligan Guide:
Always keep the c'thun buffers outside of skeram cultist or doomcaller against control, as well as shadow visions
Against aggro you want to keep shadow word pain or the 2 and 3 mana 'cthun buffs.
Generally speaking you keep their board clear and kill minions reactively till you have the mana to out-value them in the late game
If I get interaction on this I'll write a playstyle guide and tech substitutions