Mulligans
General Mulligans
Steady board and extras cards to generate instead of drawing.
Aggro Mulligans
Brann rarely becomes very useful in Aggro games so use him for trades since he's stats are decent and clear with Nova.
Midrange Mulligans
Minions to trade sticky early threats and some spells to draw cards to get ahead.
Control Mulligans
Get your C'Thun buff early and get some extra cards from your opponent instead of drawing. Hooded Acolyte and Twilight Darkmender become unplayable if you're opponent hit's end turn constantly so having a board of your own while having back-up cards is very useful.