Hearthpwn

Here's an odd little deck I threw together because I opened Sindragosa from a pack and haven't the dust to craft Frost Lich Jaina yet... and I'm sharing it because it's working surprisingly well. Getting win streaks at rank 10, anyway. 

It can beat Exodia mages because it packs an Ice Block they can't deal with. For everyone else there's a shit load of dragons. 

Your hand stays nice and full with the Netherspite Historians and Bone Drakes adding dragons, with Sindragosa adding even more punch if it's going to be a long game. Wrathion often draws 2 cards for a nice bonus. 

The deck can pivot between being aggressive and defensive very easily. Partly by which dragons you take from the historian; I've had games vs aggro where I've played 3 Alexstrasza 3 times, bringing me back from Iceblock 1 hp to 15 each time. If it looks like it's going long, you want to pick Sindragosa instead. Similarly the choice of spell from Primordial Glyph can be defensive or aggressive, and finally there's Alexstrasza herself. Go aggressive against decks you know will out value you in the long run; Jade Druid, Highlander Priest. Otherwise play it by ear =)

Malygos isn't strictly a win condition, but he is a hell of a lot of pressure. If you can bring him out with Deathwing, Dragonlord for free on your turn, then you might be able to burn a sudden win, but mostly you can drop him down, watch your opponent panic to remove him, and then drop another big dragon the turn after. And another. And another. Y'sera would do just as well, but she doesn't bring the burn potential. 

Mulligan:

Keep any 2 cost or lower card. Mulligan away 3 cost and higher. That simple.