Hearthpwn

Guide:

This one is a doozy. The Crone can deal 100 damage after she dispenses with Dorothee, a minion on your side of the board with 10 health. First I tried using a Priest deck, but what you really need against Crone is Counterspell to counter her Twisting Nether, and/or to rush her down and kill her before she uses her Twisting Nether (after which she immediately kills you, since now Dorothee is dead) around or after turn 7 (when she uses it varies).  

Overview:

Minions placed to the right of Dorothee will become taunt minions regardless of whether or not they are actually taunt minions in a regular matchup.

Minions placed to the left of Dorothee will become charge minions. 

I tried experimenting with not popping The Crone's armor, but she will still cast Twisting Nether regardless, even if you have not attacked her face at all. Time is definitely not on your side in this matchup!

Mulligan Guide: Mana Wyrm, Stubborn Gastropod (try to save him for her larger taunts and use him as a charge minion), Mad Scientist, Medivh's Valet, Arcanologist. Whatever you have in hand, lay something down on the Taunt side first to protect Dorothee from a direct minion attack.

Substitutions: A second Stubborn Gastropod can be used in place of Pyroblast. You may also want to add Daring Reporter. Spellbender is a great secret for this deck, especially if she casts Blessing of Kings on it. Gives you more minions and more tempo! Also if The Crone or an enemy minion uses an ability or spell to damage Dorothee, Spellbender comes in handy. Windfury cards would also work great on either side of Dorothee.  If Spellbender shows up as an option when you play Primordial Glyph, choose it. 

Strategy: Kill her as quickly as possible.  Even if she doesn't kill Dorothee, she will remove her with Twisting Nether sooner than you think, and after that she will do 100 damage to your face. Try to have Counterspell in place when she plays her Twisting Nether. This matchup can be tough as you need to have some board control and yet kill The Crone quickly. 

Keep laying down cards on the taunt side so they cannot directly reach Dorothee. Use your strongest attack minions to charge her face when possible.