Hearthpwn

This deck feels like a mix between Aggro Shaman and classic Midrange Shaman. Your aim is to play your massive minions as early as possible while utilizing all the spell damage synergy to activate Arcane Watcher. The insane amount of burst available to shaman really synergizes with the archetype. I currently have a 60% winrate with this deck in Legend.

Against Aggro, you can control board pretty easily (especially if you draw Lightning Storm, but it isn't necessary). Against more control-oriented decks, you can gather enough spells and spell damage to burst them from quite healthy life totals after playing your big minions early. 

Core Cards:

Arcane Watcher: a 3 mana 5/6 on curve is just too big for most classes to disrespect, especially with the threat of Squallhunter on turn 4. There are so many other ways of activating it as well (including rolling a spell damage totem), so playing it on curve has its merit.

Ethereal Augmerchant: Allows for early minion removal to play for tempo, and it's the cheapest activator for Arcane Watcher. 1 mana for 1 extra spell damage has won me the game on more than one occasion.

Squallhunter: Remember the infamous 4 mana 7/7? This guy is his little brother, with 2 less damage but much more deck synergy. On the coin? Squallhunter on 3 and Spellbook Binder the turn after. Arcane Watcher on 3 and this guy on 4. Squallhunter on 4 and Serpentshrine Portal for 5 on 5. All these situations are extremely powerful.

Lady Vashj: I'm still unsure what I think about this card. The Lady is okay since it has spell damage, but drawing the prime is insane. There are 8 spells in deck that can go face (and two Far Sights), so getting 3 spell damage on board (which is quite easy after turn 7, especially with Ancient Mage) could mean anywhere from 14 and 23 spell damage as burst. It's not your main win condition by any stretch, but a well-timed Vashj Prime draw can swing any matchup (mainly control) in your favor.

Tech choices:

Lightning Storm: Great against Demon Hunters and Spell Druid. you can also discover AoE by using Marshspawn, which is why I only run one copy. If you are not concerned with aggro, you can replace this with a Cobalt Spellkin or an Earth Shock or something.

Cobalt Spellkin: Rolling Lightning Bolt and Frost Shock really extends your reach, making it better against control. However, this is interchangeable with Lightning Storm if you are facing more aggro matchups. The 5 mana is a bit hefty when you are overloaded all the time, so I feel one copy is usually enough. 

Optional Additions:

Rustworn Initiate: Can be played on turn 2 to contest board and set up early spell damage synergy, but I don't like the unreliability of the deathrattle effect. Can replace Lightning Storm, Cobalt Spellkin, or both.

Vulpera Scoundrel: I don't like this card much because I would rather have the decent stats of Marshspawn. However, it is an option you can seriously consider.

Sandstorm Elemental: Not a bad minion, but I don't like being overloaded on turn three in this deck. Could be a replacement for Lightning Storm.

Mulligan Guide:

Against Aggro: Sludge Slurper, Arcane Watcher, Lightning Storm

Against Tempo: Sludge Slurper, Arcane Watcher, Serpentshrine Portal, sometimes Squallhunter and Lightning Storm.

Against Control: Sludge Slurper, Squallhunter, Arcane Watcher, Lady Vashj.

This deck is still in its infancy, so any improvements and suggestions are always welcome!

 

EDIT:

The list I'm running now is as follows:

-1 Cobalt Spellkin

-2 Mana Tide Totems

 

+1 Lightning Storm

+2 Escaped Manasabers

 

 

The Manasabers are there to provide a safe way to buff your board with spell damage, and occasionally you need that 1 extra mana for lethal. I added a second Lightning Storms for consistency.