c'thun druid

generally you want  to play ramp and buffers to be able to play efficient midrange minions later on. always keep wild growth. be careful with innervate you need one for c'thun combo so ifyou play vs control deck it might be a good idea not to waste it for 3-4 mana minion.

against aggro you want efficient early game cards beckoner of evil and c'thuns desciple are good examples as they let you not only buff c'thun but also to trade efficiently. ferral rage is good way to deal damage to a high threat enemy minion. wrath could be used as a removal and as a card draw mechanic. you still want to keep wildgrowth to be able to play your 6 and 7 mana taunts as soon as possible. if you can stay at quite big amount of life then it might be reasonable to keep twin emperor vek'lor since 2 4/6 taunts will in most cases be sufficient to stop aggro. also do not think about your c'thun combo against aggro decks. it might be a good idea to play brann on turn 6 if your enemy is mostly concentrated on smorking your face to get 3 4/6 taunts turn 7 and basically win game against any facecentric deck

against control ramp is really good as well as buffing your c'thun. against decks that tend to go into fatigue you might use nourish to gain 2 mana crystals. this way you can play your efficient midrange minions to dominate the board and make your enemy to waste removals. after that your combo should be sufficient to close out the game, since brann + c'thun will deal (at most, without doomcaller being used) 48-50 damage. and since against most control decks you have the board the only possible survivor after combo is warrior (theoretically, but is does not rly seem that warriors will be fast enough to gain 20+ armor by the time you use your combo, since this deck aims to close out the game in at most 15-20 turns).

against freezemage the best thing you can do is play minions and use your heropower every turn. in that case you're more likely to be able to survive the barrage of spells mage is to unleash after playing alex. also save ferral rage as a way to heal for 8.