Hearthpwn

I'm playing this deck at rank 10. It loses to nearly all Pirates (of course) and Jade Druids, but wins most of the game against Reno Mage and Reno Warlock. Winrate against Miracle Rogue and Combo Druid is about 50% (depending on which of their cards are milled out). About 40% winrate against Dragon Priest. 90% winrate against Control Warrior (obviously).

Guide:

Never play Jade Idol if you still need Reno Jackson's heal.

Keep one of the Coldlight Oracle for Brann Bronzebeard synergy.

Keep your Innervate, Wild Growth and Coin for the Gadgetzan Auctioneer turn if possible. Don't be afraid of overdraw. You have Jade Idol. In most cases where you lose, it is not because you overdrawed but rather you didn't draw enough cards to trigger Reno Jackson.

Play as if you're a combo druid, so that your opponent may speed up drawing their deck. Choose the right time to return into Mill Druid playstyle. You'll see your opponent emoting 'Astonishing' quite often.

Start to create Jade Golems with the second Gadgetzan Auctioneer. It helps you develop a strong board if your opponent has less card draws than you and thus cannot be milled to death. This is our second winning condition.

Mulligan:

Always Mulligan for Doomsayer, Wrath, and Living Roots as early game removals.

If you're sure your opponent is playing a control deck, also keep Coldlight Oracle.

Mulligan for Naturalize to remove their Mountain Giant/Twilight Drake when against Renolock.

Mulligan for all the duplicates and Reno Jackson when against aggro.