Hearthpwn

You'd think it wouldn't work, but it does. Exceedingly unique in the gameplay department, this deck is all about dancing on the line between life and death and managing your resources very carefully, setting up for unexpected massive swing turns.

The core combo is, of course, Bloodbloom and Doom. Two mana, two cards, board clear and card draw, minus 10 life. Because of its low mana cost, it is typically supposed to be used in conjunction with some of the other cards in the deck: Doomsayer, to ensure a clear board state the following turn, Violet Illusionist, to avoid the health cost, and Molten/Mountain Giants as well as Hooked Reaver-- as the combo serves to activate all of their play conditions. These can be taunted with Sunfury Protector and Faceless Shambler, and can OTK the opponent with a well timed Alextrasza. 

In the early game, your goal is typically to find your BloodDoom combo and stay alive to use it while dropping big dudes. Mistress of Mixtures, Vulgar Homunculus, Hellfire, Doomsayer, and Amethyst Spellstone are excellent tools for this. In a pinch, Bloodbloom can be used to activate other spells earlier than expected, such as Siphon Soul on an early VanCleef. Against control matchups, aim to tap into Mountain Giant to establish early threats.

In the late game, Medivh and Lord Jaraxxus are extremely powerful tools to out value almost any deck. Twisting Nether serves as a backup board clear once you are too low on cards to use Doom anymore. It is important to recognize that Doom can be used as a single target removal at this stage in the game, and may not be used at all in some matchups. 

Mulligans very much depend on matchup, with Hellfire being an essential keep versus aggro while Mountain Giants are useful keeps versus possible control. That said, almost any card that costs 4 or lower is a viable keep in most matchups; a notable exception is Faceless Shambler, which we have as a one-of as a result.

There are many cards that you can experiment with if you prefer. Twilight Drake, a second copy of Faceless Shambler, Defender of Argus, Kobold Librarian, Defile, Rin the First Disciple, Stonehill Defender, Dirty Rat, Spellbreaker, Skulking Geist, and Voodoo Doctor are all viable options to tech into the deck if needed or wanted. 

Overall, the deck performs surprisingly well against most aggro decks and pure control decks, though it struggles against combo and burn decks (since you spend so much time below 15 health). For this reason, this deck, in general, is excellent against Paladin, Warlock, Druid, and Shaman, but struggles against Rogue, Mage, and Hunter. Priest and Warrior typically run even, depending on the version.

I hope you give this underrated and fun archetype a shot!