Mulligans
Aggro Mulligans
Against aggro you want 1 ramp followed by some removal. Spreading plague alone can win games against some aggro decks so you might want to keep it. Fatespinner is also a great help with the aoe damage but you should only keep him if the rest of your hand looks good. You win your aggro matches without the quest so you should toss it away.
Control Mulligans
Against control you want to ramp up, finish your quest and cycle through your deck as fast as possible.
A combo deck inspired by the old midrange druid, which used force of natue and savage roar as their win condition. The goal of this deck is to finish the quest and get at least Ixlid, druid of the claw or leeroy for free to win the game with a cloned charge minion and savage roar. Ixlid, leeroy and savage roar alone are 18 damage (with hero attack). This deck is especially strong against razakus priest since they dont have taunt minions to protect them from the combo.