Hearthpwn

Okay, with ten legendaries, this deck looks like some kind of a joke, but watch this thing go:

Here's how it works:

Astral Communion is an incredibly powerful effect; it gives you 10 mana crystals as early as turn 1 if you play it with The Coin and Innervate.  The drawback, however, is that you have to discard your entire hand and rely on topdecking useful cards for the entire game, or at least until you get something that lets you draw.

The problem of building a deck around this card is that the cards you draw need to be powerful enough to outweigh the huge disadvantage that comes with your opponent having four or five more cards than you.  If you can drop Ragnaros, Cenarius, Ysera, or Dr. Boom on turn 2 or 3, your opponent is in trouble, even if you don't have any cards in your hand.  But if you play Astral Communion on turn 2 or 3, and you can't play anything bigger than a 5 drop for the subsequent three turns, your opponent is likely to come roaring back, as his card advantage is likely to outlast your mana advantage.

However, if the curve is too steep, you're going to be stuck with nothing to play in games where you don't draw your Astral Communion the first couple of turns, which will result in you getting your skull kicked in by any kind of aggro deck.  The problem with Astral Communion is that it fails if you play it and you can't push out a few huge minions before turn 6, but, in order to be playable, a deck that includes this card needs to have a curve that allows it to function when you don't draw into it.

In this deck, nearly everything that isn't a powerful minion is ramp of some kind, which is made possible by the new Darnassus Aspirant.  It's like a Wild Growth attached to a 2/3 body, and it forces opponents who want to go face to trade, or else cede a mana advantage to you.

Thanks to Wild Growth, Darnassus Aspirant, Innervate and Nourish, if you don't play Astral Communion you have multiple ways to reliably play a 5 drop on turn 3, a 6 drop on turn 4, or one of your 7 drops on turn 5, and, in lucky situations, your ramp ability will let you play all these cards even earlier.

The trouble is, many of the cards that make the deck work when you don't Astral Communion are really bad to draw when you do use it.  It's really strong to Innervate out Keeper of the Grove on turn 2, instantly killing an opponent's Knife Juggler and leaving a 2/4 body in a good position to trade with at least two more aggro cards.  But you don't want to see either of those cards the turn after your Astral Communion.  

Aviana is an incredibly strong play if you have several cards in your hand and she combos extremely well with Innervate, creating a tremendous late game combo for a card that has historically been a liability to draw after turn 7. But it's not good to draw her into an empty hand, and either have to play her onto an empty board, or else spend a turn doing nothing as your mana lead dwindles.

Chromaggus, Nexus-Champion Saraad and Justicar Trueheart will, hopefully, help a bit with these problems.  

Drawing one Swipe or Keeper of the Grove after discarding your hand to get 10 mana crystals is a pretty bad outcome, but playing 2 of those 4 drops with a little help from Chromaggus can be devastating.  And if Chromaggus eats a silence before he draws you any cards, he's still a 6/8 body, and your opponent won't have the silence for Ancient of War or Ysera.

Nexus-Champion Saraad and Justicar Trueheart give you a lot of flexibility, because you can either get them out using traditional ramp methods as soon as you can meet their costs, or you can play them after Astral Communion along with your hero power for significant extra value.  The improved Druid hero power is very good, and nearly as good as a card, so having that every turn helps a lot to make up for the tempo loss that comes with top-decking some of your less-powerful cards.

Mulligans, and when to cast Astral Communion:  Generally, you should keep anything that ramps, and you should mulligan everything else.  The hand you're always trying to get is Innervate + Astral Communion, and if you get these cards by turn 2, you should always astral.

If you are able to cast Astral on turn 3 with Wild Growth or especially a Darnassus Aspirant in play, you should generally cast it, since your opponent is likely to kill the Aspirant and take that mana crystal away if you don't.  However, if you are going to be able to drop a 5 drop like Druid of the Claw on turn 4 after a Wild Growth, you should probably do that instead.  You do not want to risk discarding a strong turn-4 play to use Astral Communion on turn 3, only to get stuck drawing Innervate or Darnassus Aspirant the next turn.

Do not use Astral Communion if you can't get it out before turn 4, unless you have no other ramp and nothing but 8 and 9 drops in your hand.  Regardless of what you do in a situation like this, you're probably losing though.

EDIT: Removed a Big Game Hunter, who is terrible to draw into after Astral Communion.  Replaced him with Nefarian for now, but seriously considering using Icehowl, who serves a similar function to BGH in an Aviana combo if you reach endgame without using Astral Communion, and is a tremendous card to topdeck on turn 3-5 if you use it.