Hearthpwn

Card Choices:

EDIT: Added Sen'jin Shieldmasta, Second-Rate Bruiser, and Dark Arakkoa because this deck needs more bodies.

Mark of Nature: Extremely flexible card and borderline OP when used with Fendral Staghelm. Able to slow down aggro a lot when used as a taunt, excellent source of damage when used for attack. Combining this with Faceless Manipulator can swing the late game. Play on one of your minions and copy, or copy an opponent's minion and buff it with +4 health and taunt.

Faceless Shambler: Less flexible than Faceless Manipulator, but works OK in this deck. Works really well in conjunction with Force of Nature or Arcane Giant (or both!).

Faceless Manipulator: Another very flexible card. In this deck, can be used to amplify burst damage to end games, can be used to copy beefy minions (Arcane Giant, Ragnaros, Ancient of War), great value at 5 mana, and again great to combo with Mark of Nature.

Lunar Visions: Not outright better than Nourish in terms of flexibility and card draw, but has some practical uses in this deck. Kun/Aviana deck doesn't need it because of the reduced cost from Aviana. Nourish is also a better option there because of the need to ramp to 10 mana ASAP. But it sets up the potential for some favorable situations here, where the ramp is more crucial between turns 5-8 and reduced cost minions become more valuable. Additional burst damage (3-cost Faceless or Druid of the Claw which gets Emperor'd down to 2), turn 6 Ragnaros or Ancient of War, a reduced cost Gadgetzan allowing for easier card draw. At the very worst it draws one less card than Nourish, which is acceptable since we're rarely card dead.

Azure Drake: Better tempo than Emperor Thaurissan, currently taking the only flex spot in the deck.

Emperor Thaurissan: Not necessarily crucial to this deck, but very valuable and flexible. Sets up burst potential, adds value to the ramp turns 5-7, makes it easier to cycle with Gadgetzan. If there's 5+ cards in your hand you're getting value no matter what. Some burst examples:

• Druid of the Claw + Faceless Manipulator + Mark of Nature = 10 mana, 16dmg
• Feral Rage x 2 + Swipe x 2 = 10 mana, 16dmg
• Azure Drake + Bloodmage Thalnos + Swipe x 2 = 10 mana, 12dmg 

Ragnaros the Firelord: OP.

Arcane Giant: Similar to Jade Druid, there really isn't a reason not to run two of these if our ultimate goal is mid- and late-game pressure. This deck runs 18 spells, plus 2 from Raven Idol (you're choosing spell 90% of the time), plus maybe 2 from Wild Growth after turn 10. Excellent target for Faceless Manipulator if you can drop it fast enough or cheap enough.

Mulligan:

If there's any interest I can write a detailed guide, but the TL;DR is play very defensive versus Aggro (keep removal spells, Innervate, Sen'jin and Fandral), focus on board control and tempo versus Tempo/Midrange (keep Wild Growth, Innervate and value minions), and be very aggressive versus Control (you're winning this game turns 7-12).