Hearthpwn

I have no clue how competitive this deck is, simply because one of the vital cards in its combo is not yet released (as of my writing this).  Also, this is more of a brainstorm then an actual list; if you want to try to use this deck competitively, you'll want to add a lot of removal.  That said, the aim of this deck is to stall until you pull together the required combo pieces; once you have them, it would be difficult to lose.

The fundamental combo is using a Shadowcaster on another Shadowcaster.  By itself, this isn't particularly threatening; you just get a short-term supply of 1/1s for 1.  Now add in Brann Bronzebeard.  If you use Shadowcaster -> Brann and then Shadowcaster -> Shadowcaster, you now have 2 1-cost Branns, and 2 1-cost Shadowcasters, which is enough to repeat the combo whenever you want.  Once you get to this stage, you will be able to fill the board with 1/1s every single turn.  Now, what can we add?

The first possibility is Hobgoblin.  Once we have our Brann + base combo, we can play Hobgoblin, Brann (1), Shadowcaster (1) -> Hobgoblin, Shadowcaster (1) -> Shadowcaster to refill your Shadowcaster supply, and possibly Shadowcaster (1) -> Brann if you would otherwise run out of Branns.

From here, we have the play HG, HG, Brann, SC -> HG, SC -> Brann, SC -> SC, SC -> SC.  At a cost of 7 mana, you get a 1/1, a 3/3 and 5 5/5s.  More importantly, you can do this every single turn for the rest of the game.

So what are the rest of the cards here for?  Well, each one can be incredible in certain situations; when you draw a card, you can run it through the cycle of 1-costing (Card, Brann, SC->Card, SC->Brann (optional), SC->SC, SC->SC (optional)), so from now on, you can play it when the situation is right.  Not sure what I mean?  Let's look at a few examples:

Kidnapper:  Once you've run it through Brann, KN, SC->KN, SC->Brann, SC->SC, SC->SC, you have what's basically a 1 mana, 1/1; return a minion to its owner's hand.  Since you have a continuous stream of 1-cost cards, you will always be able to get the combo off, so you now have an unlimited supply of Saps.  Actually, it's much better than Sap- 1 mana less, a free 1/1, can target 'untargetables', and can be used for bouncing your other cards if you feel.

Emperor Thaurissan:  This can have a couple of uses; first, to get your combo off the first time (and generally, you should use this card for that purpose).  However, if you draw into it later, it can be game ending- you have an endless supply of 1-cost cards...  Why not get 5-10 free cards per turn?

Faceless Manipulator:  Hmm...  That's a nice card you played there.  I'll take it.  Since you should always be copying minions with FM, reducing its stats to 1 doesn't change anything.  However, if you want this to work, you'll have to play it without copying anything the first time...  Clear the board, and run it through the cycle; you now have an unlimited supply of 1 mana Faceless Manipulators.  Basically, if your opponent plays 1 Rag, you should counter with 5.  Generally, having this option means your opponent can no longer play any large minion.

Antique Healbot:  You cannot die.  Why?  1 mana, 8 health, unlimited use.  i.e., you win the game.

Gormok the Impaler:  You can very easily get 4 minions out, so this basically reads "1 mana, deal 4 damage".  Again, unlimited use.

Edwin VanCleef:  Do I need to explain this?  Unlimited use VanCleef with unlimited 1-mana cards (that can be reduced to 0 cost with Thaurissan).

Anyway...  If you get your combo out, pretty much the only way for you to lose is if the opponent can kill you with just charge + spells (assuming you don't have Healbot).  But wait!  How do you actually get the combo?

Well, this is where you choose how many combo cards you want to switch out for removal; the more removal, the more likely you are to live long enough to play the combo.  I'd estimate that dedicating half the deck to removal would be ideal, though I obviously can't test it.

The other ways to speed up your combo-getting revolve around card draw, Gang Up and stealth; you want to use the card draw to get the required cards for the combo to work.  The stealth is used so that you can have 1 combo piece safely on the board for a turn, so that your opponent can't mess up your combo.  Thaurissan fits into a similar role, because if you have the whole combo in your hand, you'll be able to play it in one turn without stealth.  Gang Up is used to increase your chances of finding one of the necessary cards, and to enable the combo even if you lose a Shadowcaster.  Shadowstep is also very valuable, as it protects your minions, but allows you to reduce the activation cost of the combo.  This also allows you to work with just 2 of the combo cards (though 3 is the requirement for game-breaking).

Replacements?  As long as you have 2 Shadowcasters and Brann, the deck can work.  The most important cards aside from those are Shadowstep, Thaurissan and some of the stealth cards; I don't advise running the deck if you're missing more than one of those.  Aside from that, spam any strong battlecry effects (or strong effects in general) and card draw, and balance with a whole lot of removal.

And most importantly, have fun!