Hearthpwn

Malygos Druid: 50/50 or even 60/40...

They're really slow and have like 2/4 minions outside of the combo pieces so you can afford to be greedy in the mulligan.... If you see the DK keep it cause you'll need healing to survive... Also I'd keep Gluttonous Ooze cause the most popular lists don't run Rummaging Kobold and destroying the weapon severely hinders their damage potential and also slows them down a lot.... Other cards I'd consider keeping are Polymorph and above all Skulking Geist cause those are game winning against Taunt Druid and Geist also denies them removal in the form of Spellstone and Naturalize.... Keep in mind that without the weapon the maximum damage they can do from hand is 22 while if they get their 20 mana turn the damage ranges from 32 to 51 so little Ooze is your friend here....

Taunt Druid: 70/30...

The mulligan is basically the same as above the only difference being that if you play Geist and have Polymorph in hand is gg otherwise you have to hope Witching Hour doesn't resummon Hadronox.... In case draws screw you over and you have to deal with a full board try hold onto Blizzard and Dragon's Fury cause they're only cards that can deal with those board states....

Token Druid: 30/70...

Horrible MU,I have yet to win a game against this Deck... Unless you get 2x Dragon's Fury there's no way you can clear their board and you'll most likely get OTKed even from full HP and some armor so it's not even worth trying to mulligan for this MU just keep the cards you'd keep against Taunt or Maly.... 

Recruit Hunter: 40/60

I find this MU to be really draw dependent,if they get charges from their Deathrattles you're pretty fucked if they don't and they have to pay the actual cost for those cards it's ok.... Polymorph is your best friend here and Meteor] isn't bad either.... Also if you get Arcane Keysmith try looking for Spellbender to deny Hunter's Mark/Play Dead or Mirror Entity to pop their deathrattle (and sometimes even get a random 2/2/Lich King depending on what card he played) and get rid of the minion before he can get value out of it....

Spell Hunter: 60/40

Unless they get a nuts start and you draw really bad this should an ok MU.... If you see Jaina keep her cause you'll need healing and then just AOE their board to pump Alanna and enjoy smacking the guy's face with 5/5s cause unless they highroll the DK they have no way of dealing with a board like that....

Aggro Mage: 20/80...

One word Counterspell.... That card is your nemesis and it makes this is your worst MU.... The fact that they changed how the card works in the latest patch made things even worse,if possible,cause now you don't get armor from Arcane Artficier if your spell gets Countered.... If they play a Mana Wyrm on turn 1 and you don't have The Coin you can concede.... I lost even when they started playing minions on turn 4 and I oozed their Aluneth the turn after it was played.... Ignore this MU and hard mulligan for Jaina everytime you see a Mage cause you'll need her for the mirror...

Control Mage: 50/50...

1. HARD MULLIGAN FOR THE DK! Toss anything and everything cause you need to have Jaina on curve,if you have The Coin try to hold onto it to play her on turn 8.... I can't explain how frustrating it is to try to keep up with those Elementals when you don't have Jaina.... In fact if there's on thing I hate about this Deck is its reliance on drawing the DK to win....
2. Unless you really need to don't draw any card cause this will go to fatigue for sure....
3. Also remember to hold onto Blizzard and another AOE otherwise Alanna will destroy you....
4. Prioritize playing Dragon's Fury over other cards when possible otherwise you'll find yourself with a dead card later in the game....
5. Don't hesitate to ping your own minions so that your opponent can't AOE+Hero Power to kill them....
6. Don't play Ooze for Tempo,it's not worth it and you might need it to destroy Frostmourne (I learned that the hard way...)
7. Be greedy with Stonehill Defender...
8. Counterspell/Mana Bind are your best friends so pick them from Arcane Keysmith... Spellbender is okaysh as well and Vaporize and Ice Barrier are also somehow decent....

Odd Paladin: 60/40

Hard mulligan for Dragon's Fury cause the card is game winning.... The only burst damage they have are Leeroy and Vinecleaver so if you manage to keep the board clear you're safe even at relatively low HP.... You can keep Doomsayer but there's a high chance it'll get silenced but it's still your best turn 2 play.... Raven Familiar and Stonehill Defender aren't bad either.... If you have a good starting hand you can even consider keeping the DK... 

Combo Priest: From 70/30 to 30/70...

I really wonder when stupid Inner Fire will be HOFed and I can't wait for that abomination that is Shadow Visions to rotate out...  Horribly draw dependent MU... If you get Skulking Geist you should be ok but until you draw that remove every single minion he plays and attack into them if you can't kill them otherwise you'll likely find yourself smacked to death by an ∞/∞ Northshire Cleric...

Mind Blast Priest: 40/60...

Once again hard mulligan for the DK... Basically any other card other than Jaina and Arcane Artificier (out of which you need to get a ton of armor to survive) are useless here.... You can try getting Counterspell for the swing turn but that's unlikely to work,still worth a shot though since there's not much more you can do.... Don't play Alanna before they play the DK.... If you get offered Rotten Applebaum from Stonehlll Defender get it cause that 4 HP might make a difference.... 

Miracle: 70/30...

Look for Polymorph/Voodoo Doll in the mulligan cause you'll need them for "3 mana 4/4 kill me or I'll snowball out of control" and for EVC... Also Oozing their dagger on turn 3 is good cause it'll force them to redagger or play something less snowbally then HCT.... Unless absolutely needed hold onto Flamestrike/Dragon's Fury to deal with their spiders.... If you think you can afford to tank some damage you can let Gadgetazan Auctioneer live to try to get more value out your AOE.... Skulking Geist is your friend cause it denies them burst damage.... 

Odd Rogue: 60/40

Mulligan for Dragon's Fury/Polymorph/card]/[card]Voodoo Doll.... Stonehill Defender and Doomsayer are also good but keep in mind that the latter might also get countered by Void Ripper other than being silenced....  As above turn 3 Ooze is annoying for them cause if forces a change a of plans.... From Arcane Keysmith Ice Barrier and Vaporize are your friends especially the former.... Explosive Runes and Spellbender/Counterspell aren't bad either....

Shudderwock: ?/?

Basically it all comes down to whether or not Shudderwock gets bounced to his hand.... If it does you lose if it doesn't you have a fair shot a winning.... Mulligan for Jaina and try to hold onto Blizzard to deal with the Shudderwocks in case RNG screws him over.... Of course if he plays Acolyte of Pain and you can make him overdraw don't hesitate to do so....

Cubelock: 30/70...

The main problem here is that Warlock is pretty common and it has 2 radically different kind of Decks.... Slow ones like Cube and Even and a fast one in the form of Zoo so mulliganing when you see a Warlock is pretty difficult.... The only card I'd suggest to keep everytime is Doomsayer as it can stop a turn 3/4 giant as well as slowing down Zoo.... If you're feeling lucky and want to mulligan for Cubelock you'd look for the DK,Ooze (Their stupid weapon is one of the most snowbally cards out there) and Polymorph/removal for a turn 4 giant.... After turn 4 be really careful when playing Doomsayer cause he might use Carnivorous Cube and screw you over.... I'd much rather transform a Doomguard other than a Voidlord to reduce their burst damage and also dilute the DK pool.... 

Even Warlock: 50/50...

Same as above if you feel like mulliganing for Even look for the DK/removal for their turn 3/4... Keep in mind that they have more high HP minions (so Meteor is good in early stages of the game) than Cubelock but less burst damage.... Avoid pinging them in face as it just helps them get to 15 HP to trigger 4/4 effect and you don't have any burst to finish them off.... They don't have any absolute "crap" minion so Mirror Entity or alternatively Explosive Rune from Keysmith are good picks,same goes for Counterspell and Spellbender cause they don't have any really "useless" spell to trigger them.... Try to keep Blizzard/Dragon's Fury for DK board...

Zoo: 60/40...

I find the current version of the Deck to be more brick prone the previous ones but it compensates cause it can have some ridiculous starts and you might roflstomped on turn 4.... Anyway,as usual against aggressive Decks Dragon's Fury/Doomsayer are your best friends.... Raven Familiar is also good as it will likely trade with one of their minions while drawing you a card.... Stonehill Defender is also decent,just make sure you pick whatever cheap minion it gives you (even useless stuff like Wax Elemental is fine as long as it absorbs damage)... If you have the aforementioned cards (especially the AOE) you can keep Jaina or even Alex as you'll need that healing later on....

Quest Warrior: 50/50...

The good old coinflip hero power who doesn't like that? Many people think this is a bad MU for the Deck but I personally find it to be pretty even.... As with any slow Deck hard mulligan for the DK you'll need the healing and also the Freeze effect really screws over Warrior.... Unless you're drawing to increase the chances of drawing Jaina there's no reason to play minions... it's much better to play them after he finishes the Quest to avoid getting pummeled in the face.... Feel free to "waste" AOE as he doesn't have that many minions.... Try picking high HP minions from Stonehill Defender so that he can't one shot them with his hero power.... Frozen Clone is good here cause not only it'll give you something to play but will also protect your face from damage..... Counterspell is really good here especially if played Skulking Geist earlier.... 

• Doomsayer:I'm playing this cause it's the one 2 drop that isn't useless late in the game but if you're facing Aggro or run into too much silence/Void Rippers or even if you're on a budget Plated Beetle is an excellent alternative...
• Bright-Eyed Scout:I admit I'm mostly using this for the highroll potential.... It's hilarious when she draws an 8 or 9 drop to be played on turn 5.... It's certainly the most replaceable card in the Deck,you could run Witchwood Piper or even Saronite Chain Gang,objectively they'd probably be better than this card and increase your winrate so don't run this card...
• Alexstrasza: I always feel like this Deck needs more healing and Alex is the best way to do that.... Yes,she's clunky but can also be game winning (against Zoo/Odd Rogue/Paladin and Hunter).... I suppose it's a matter of preference,you can easily replace her with more early game,like Tar Creeper,or with Baron Geddon or even more card draw....
• Dragoncaller Alanna: I have mixed feelings about this card.... She's utterly useless against Warlock/Priest/Rogue and Paladin but singlehandedly wins the game against Hunter and Mage... I admit I'm a bit biased towards her (She summons a full board of Dragons I just can't get myself to replace her) but I'd keep her until the meta speeds up, cause you know your opponent needs to have AOE to deal with her it's not likely but they might not have it and lose on spot.... But she's by no means necessary for the Deck so there's no need to "waste" dust if you don't have her...
• Sindragosa:Horribly slow but there's no other card that synergizes that well with Jaina and that gives you so much value... At first I wasn't convinced but now I don't think I'd replace her.... The only other card that I can think of the can generate the same amount of value is Elise but she doesn't give you Elemental and she'd be a dead card for most of the match....
• Baron Geddon:The most notable exclusion from the list,I just can't get myself to like this card.... It's good against Paladin and it heals you after you played Jaina but what else? Most of the times it sits in my hand cause I don't want to take face more face damage and the fact that it has 5 HP sucks.... Again that's a matter of opinion I guess some people would have no problems running him in place of Alex or Alanna....
• The Lich King: I'm running this just cause I hate losing slow MUs (especially the mirror) I personally think it's not that good of a card.... It's basically "Battlecry: Draw a Death Kinght card" and absorb some damage or removal,the thing is that there are like 3 good DK cards out of the 8 he gives out so half the time you sit there with a card that beside clogging your hand deosn't do much... I'd use something else the problem is half the high cost cards suck hard and this is by far the best of them.... If only Deranged Doctor was a Battlecry....
• Frost Lich Jaina:She's the reason this Deck exists,you can't replace her and if  you don't have her just gather some dust and craft her so you can annoy the hell out of your opponents while spamming "Bow to your Queen!"...
• Arcane Keysmith:At first I wasn't convinced but Mage Secrets are mostly good and the pool is so small that if you play this card with a specific Secret in mind you'll get it 80% of the times.... If you're low on dust you can easily replace this card with more taunts or card draw but if you play Mage a lot I'd suggest crafting it.....   Also +1 to this card for being an Harry Potter reference...