Hearthpwn

This is the first time I reached Legend, and I achieved it with this deck.

I tried many many forms of Maly druid, but none of them fits the current meta. I'm not saying they are not playable, but I was grinding with them without any success.
I was rank 4 earlier today when I added Baron Geddon mostly against Shamans, hunters, Warlocks (actually it's great against everything as You have many low cost spells to reduce the enemy minions to 2 health), and I got to legend from rank 4 with 2-3 loses.

Changes: 

1. Removed 1x Mulch, Added 1x Mire Keeper
Reason: I don't meet Reno locks / Rogues anymore, and I face more and more agro decks.
2. Removed 1x Mire Keeper, added 1x Feral Rage
Reason: Mire Keeper often stays in my hand for several reasons, and it is simply not a good card in lategame. Even if I ramp a little slower, Feral Rage often saves the day, and then I can make a big comeback.

Thanks to Fur0 for the gameplay video!

Mulligan:

Wild Growth, Innervate and Mire Keeper are Your number 1 mulligan priority. You can keep 1 copy of Raven Idol also. 
Basically, You see any of these cards in Your hand, keep them, and replace the rest. 

Sometimes it's good to keep Fandral Staghelm if You already have the great starting cards on hand, or if You can play it in T1 with Coin and Innervate. Remember it's not only good for Your chose one cards, but it's also great if You can play it early and it forces Your opponent to use many important resources on it.

There are some mulligan suggestions against each class, read below: 

Warrior: I usually keep Harrison Jones to deal with the weapons. If You are sure You go against the new pirate face warrior, consider keeping Living Roots and playing it on T1. Other then these, general mulligan applies.

Shaman: Very hard matchup. Always keep Harrison Jones! You can Innervate and coin into it if the opponent plays it early. I generally play it ONLY if it removes Spirit Claws from the opponent, even if I have empty turns where I could play nothing else. If I already have a Wild Growth in hand, I also keep Wrath to deal with some early-game danger. 

Rogue: Keep Harrison Jones. Their weapon is not a real threat but still You can draw up to 2 cards from it. Look for a Mulch, in Raven Idol! Their Edwin VanCleef can be very-very scary.

Paladin: General mulligan rules.

Hunter: This will be Your hardest matchup. Always keep Living Roots and play it on T1. Keep Wrath if You have Wild Growth in hand. If You already have a T1 card and a Wild Growth, keep Fandral Staghelm and play it on T3/4 (if You don't have Mire Keeper to play it on T3/4 of course). Generally You have to ramp up quickly against Hunter, so I suggest playing Your mana crystal gaining cards in the early turns, even if You take many dmg, so You can control the board easily later. Generally I am at 10-12 HP on T4-5, but then You can easily clear the full board, and play a Feral Rage in the same turn for 8 armor, or play an Ancient of War to protect You from more dmg. 

Druid: General mulligan rules.

Warlock: I meet now Zoo lock mostly, and it's not easy to deal with them. Keep Living Roots always, and keep Fandral Staghelm if You already have Wild Growth in hand, so You have a nice 3/5 body to play on T3/4 if You don't have Mire Keeper. 

Mage: If You already have Wild Growth keep a Wrath or a Living Roots so if You are facing tempo, You can kill the scary 3/2 targets. 

Priest: General mulligan rules. 

Guide:

Your number 1 priority is to ramp up quickly with Your mana Crystals, because You mostly have expensive minions, and You need that mana to play them.

Some basic rules:
- T1 Raven Idol, T2 Wild Growth, T3 Mire Keeper is the best scenario. 
- Don't coin into Wild Growth in T1, if You would only hero power in T2. Only do it if You already have a card for T2.
- If You don't have Wild Growth, Innervate into Mire Keeper in T2. 

This is all for now guys, if You need some more info, please write in the comments! 
Please note that You need to get used to a deck before You can start profiting from it. It usually takes me at least 4-5 games to get the feeling of the deck I'm playing. 
Have fun playing, and good luck winning :)