Some fancy roleplay in the spoiler:
Naturalize the Nightmare
N'Zoth, the Corruptor has penetrated in the Emerald Dream, ravaging and befouling it, reviving the Nightmare!
Our Shan'do, in his desperation, has turned into Malfurion the Pestilent, Spreading Plagues in order to contain the Nightmare, at all costs. He is risking to corrupt the balance between Life and Death, against the madness of the Old God.
But there comes Arch-Druid Hamuul Runetotem! He will know which way to choose in the Branching Paths.
This is at its core a Control deck. Unlike Mill Rogue, this Fatigue/Mill Druid is favoured against Aggro, while it needs careful planning for Midrange and Combo decks. You have tools for nearly any situation, but you need to use them wisely.
Armor power helps a lot in either outlasting Aggro, or making you just too tough for slower decks to kill.
As for any other Control deck, the key is to ALWAYS know your opponent: being able to foresee what is available to them is game-winning, for you can optimise your resources into maximum value. Typical example is knowing when to use Doomsayer, which can be either used as pseudo-taunt against many pings, or to buy full turns against empty boards in the middle of the game.
Against any: armor up and taunt (but since your cards are versatile, always proceed wisely, timing is fundamental).
Against Aggro: Hero power during first turns. Grove Tender for mana. Taunt up. Never double-draw, unless absolutely necessary. They will eventually run out of steam, while you're safe and can recover with more Armor.
Against Naga Giants decks (typically Hunter and Warlock): NEVER double-draw. In mulligan, it is wise to keep sludge belcher or spreading plague, change the rest to look for poison seeds, which is the key card of the match (unfortunately, you can hardly tell what kinds of Hunter or Warlock they are during Mulligan).
Against any decks that tend to draw a lot, such as Exodia Mage, non-Zoo Warlock, Priests, etc: try to hide your Mill power, and when they are at full hand, go hard with Naturalize, Grove Tender and Coldlight Oracle: hopefully you burn some of their key cards and seal the game.