Hearthpwn

Peak Rank: Legend 138 NA
Twitch: http://www.twitch.tv/crusherhs

Mission:  Play minions with strong stats for their cost, but with silensible drawbacks: Zombie Chow, Ancient Watcher, Eerie Statue, and Fel Reaver.  Then silence these minions with Wailing Soul and Keeper of the Grove or give the ones that can't attack taunt with Sunfury Protector.  Use this huge tempo gain to dominate the board early; push damage through in the midgame; and quickly finish the match with the classic Druid combo, Force of Nature + Savage Roar.

Gameplay: Videos of me and others piloting the deck.

Me:  http://www.twitch.tv/crusherhs/v/37454887 and
         http://www.twitch.tv/crusherhs/v/38829432
Nat:  https://www.youtube.com/watch?v=6SGox5D1NQw&feature=youtu.be
Kristophesaurus:  https://www.youtube.com/watch?v=IRKJdcQ41Sk
Eik0w: https://www.youtube.com/watch?v=I4tl9M4pWH4 (en français)

Story:  Many claim that Druid has only one style: play the best minion at each mana cost on curve (or ahead of it with Innervate, Darnassus Aspirant, and Wild Growth) and finish the game with combo.  There is little focus on synergy between the minions.  While all these cards are often key components, I have found Druid to be very flexible, and in the past, I have made legend with Egg Watcher and Deathrattle variants.  In the past couple seasons, I experimented with many more ideas including mill, Malygos miracle, and fatigue (an idea from a friend, Atropine), but I couldn't get any of these to the competitive level I wanted.  Silent Druid separated itself from these other ideas by having immediate success on ladder.  With only a little tweaking to my original list, I climbed from rank 12ish to legend.

Meta: The success of this deck rode on the back of its strong matchups against the three most prevalent heroes on my ladder climb, Warlock, Mage, and the infamous Paladin (almost exclusively secret builds).  From rank 5 to legend, I had 63%, 59%, and 59% win rates against these heroes, respectively, and together they made up 61% of my opponents (32% Paladin alone).  In the current meta, the dominant strategy is to play the strongest minions possible on curve, but this deck exceeds the ability of any other hero in this task.  Silent Druid can also be extremely aggressive, often reducing the opponents health to dangerously low levels before they have an opportunity to execute their power plays, e.g. Mysterious Challenger.

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 Mulligan:  As is often the case with Druid decks, starting with a well curved hand is more important than keeping any specific card, so the following are just good guidelines on what to keep.  Don't crowd your hand with too many cards at the same mana cost.  Don't keep two minions unable to attack if you have no activators.

Keep: Innervate, Zombie Chow, Ancient Watcher, Darnassus Aspirant, Sunfury Protector, Eerie Statue, Keeper of the Grove, and Wailing Soul (last one preferred over Keeper if you have both).
King Mukla:  Keep against all but Mage, who can make too much use of those Bananas
Swipe:  Keep against Paladin, Warlock, Mage, and Hunter
Fel Reaver:  Keep if you feel confident in your early game (a couple 1/2 drops or an Innervate or facing a slower hero like Priest, Druid, Warrior, or Rogue).
Druid of the Claw:  Keep if you have an Innervate and 1 or 2 drop.

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Matchups: Listed from statistically best to worst with winrates based on all games played from rank 5 to legend rank 988.  All matchups faced fewer than 6 times are grouped in the "Other" category.  Some are linked to example games I played on stream.

Hunter (6/6 100%):  Ride superior tempo and Swipe to victory.
Aggro Shaman (7/9 78%):  Play defensively until you get a big threat down.  You're on a clock, so at some point you have to do damage.  You won't be able to heal much, but they won't be able to at all.
Reno Warlock (6/8 75%):  It is difficult for the Warlock to time Reno Jackson, since he has to be worried about combo.  Keep moving their health in range without going all in.  Beware the full clears with Shadow Flame and Twisting Nether.  This deck is fast enough that he often won't reach Reno in time.
Other (16/23 70%):  An unusually good mark against the randos.  This deck has some very specific weaknesses, like full clears and cheap hard removal, that many heroes just don't have access too.
Secret Paladin (18/33 55%): I was doing a good bit better against Secret Paladin until the upper ranks, but this is still a pretty good mark against the deck to beat.  Swipe is key especially to clear a Muster for Battle and/or clear the board for an Eerie Statue.  You do have to clean their board up a little more than against other decks with all the buffs, but your minions are much larger and it can be difficult for them to stop the damage.  Check for Nobel Sacrifice before attacking with a threat, and try to get enough damage through before he plays Mysterious Challenger so that he can't recover even with the huge tempo swing.
Zoo (6/11 55%): This is an interesting match.  it's critical to have some early plays turns 1/2 to not get overrun, but in the next few turns you can easily pull ahead with your large minions and a well timed Swipe.  Beware though, eventually his card advantage will bring him ahead again.  Luckily all of the tapping will likely move him into lethal range.
Tempo Mage (6/11 55%):  This seemed tougher than the winrate would suggest, by a little, maybe a 50/50.  It mostly comes down to what the Mage draws, for instance Fireball and Flame Cannon are huge.  If you can ever take control of the board, it is difficult for the Mage to climb back in.  More than any other matchup up you should be looking to clean up enemy minions, especially those with persisting effects, like Sorcerer's Apprentice and Flame Waker, because Tempo Mage also has card draw problems.
Control Warrior (3/6 50%):  This one also felt tougher than the winrate would lead you to believe.  I think you just have to gamble that they don't have brawl in order to do enough damage.  If however they don't and maybe are missing some key early removal like Fiery War Axe or Death's Bite, you have a really good chance.
Midrange Druid (4/9 44%):  This matchup felt pretty tough, but not entirely sure why.  Unfortunately I don't have a lot of insight either.  There's a lot of counting and players alternately and narrowly staying above a lethal combo or just barely moving the opponent's health into range.
Control Priest (3/7 43%):  A difficult matchup mostly because of all the strong AoE, and cheap removal of your big threats.   Light Bomb and Auchenai Soulpriest + Circle of Healing are brutal while even Holy Nova and Excavated Evil can clean up your board.  Shadow Word: Death early and Entomb put the nail in the coffin.  Surprised I eked out three wins here. 

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Some Card Choices:

King Mukla:  Let's start with the elephant... errr, gorilla in the room.  First, Druid doesn't have any agressive 3 drops without a deathrattle (Wailing Soul anti-synergy).  Mukla is a 5/5 for 3, well above curve, with the downside that he gives your opponent 2 Bananas.  These bananas, cost 1 each though, and 1/1 for 1 mana is not very efficient.  Granted, this gives your opponent a lot of flexibility, so there is a serious downside here, but in order to play it, your opponent has to spend a mana, and most importantly, not play on curve that turn.  In a meta where playing minions on curve is key, Mukla gets a lot stronger.  I'd give it a shot, but if you don't like him, or don't have him, he can be replaced with a Druid of the Flame or perhaps a Living Roots.

Big Game Hunter:  An oddly situational card for this deck, but the potential tempo swing is just too large to forego. Dr. Boom is still king, and BGH is Druid's only answer.

Druid of the Claw:  I think this card is a very natural fit for the deck, but I'll talk briefly about which form to use.  This card is very versatile.  If you Innervate it out early you'll typically want taunt form.  If you have some weak minions you need to protect, taunt form is useful again.  Sometimes, he can charge a key minion, maybe even leaving a body behind, like against a Flamewaker or an Armorsmith.  Most other times, you'll prefer charge directed at face as you whittle your opponent down in the midgame or as a finisher with Savage Roar.

Fel Reaver:  Another large body for its cost.  The downside isn't that bad.  There's little card draw in this deck, and you are hoping to end the game fast, so you'll rarely get to fatigue.  If he is starting to cause problems in a game, you can always silence him, but don't be afraid to play him even without a silence.  Sometimes you will get burned, but it is more often the right play.  I do only play one though, because Two Fel Reavers could easily bring you to fatigue.  It would also make the deck a little crowded in the 5-slot where the versatility of Druid of the Claw is very handy.

Sunfury Protector: The synergy makes sense, but why this over say Ironbeak Owl.  First, having some extra taunt in the deck can be really useful.  Sitting your weak minions behind a monolithic taunts can help you set up a strong Savage Roar.  Second,  Sunfury is an okay turn 2 play, and this deck needs to get off to a solid start to execute its game plan.  Finally, "activating" two minions as opposed to just one can be huge, even if they can't attack.  Comparing to Defender of Argus, this deck already has a lot of 4 drops, and the extra +1/1 isn't a big deal compared to the large stats of the key minions.  The minion may not even be able to attack, further limiting the usefulness of that buff.

Zombie Chow:  This card is a little surprising considering how aggressive the deck is.  The synergy with Wailing Soul is there, but even if you don't manage that, in the early game it is huge.  For the first 4 turns you're usually looking to hold board control, which is beyond the typical life span of this minion, giving little benefit to your opponent.  Critically, it can preserve your Darnassus Aspirant a couple key turns while you set up your silence combos.  2/3 stats for 1 mana is pretty good.

31st Cards: In mana order, not necessarily usefulness order, Living Roots, Ironbeak Owl, Druid of the Flame, Ogre Brute, Harrison Jones, and Loatheb.

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Parting Advice:  Be aggressive!  This deck is more of a hybrid between Aggro and Midrange.  You will run out of cards.  Two Ancient of Lores can only take you so far.  Usually somewhere in turns 4-6 you should switch to primarily going face, at most using your weaker minions to protect your threats.  Count the damage in your hand carefully and often.  If you have a chance to put yourself in range of lethal with combo, you probably should take it.  Make your opponent have the answers.  Eventually they'll crack and you'll hit them for 7 or 8 damage.  Then later you will have other opportunities to draw into the damage you need to close it out.

Want more tips?  Come check out my Twitch channel.  Thanks again to Blackwolf for editing and general advice on the deck.  Have fun silencing and crushing.  Then let me know how things go!  Questions and suggestions are very welcome.