Hearthpwn

General notes:

The good news when playing against a warrior is that they do a lot of their removal via weapons. Nigh all minions you play are very sticky, requiring two weapon hits to be removed. You need however be prepared for whirlwind effects that would kill off the creatures you spawn, mostly the 1/1's from the Haunted Creeper and the 2/1's from the Dragon Egg. A well played Power of the Wild can win you games in that regard.

Mulligan:

You can keep Savage Roar - without it, winning is very hard.

Patron Warrior:
Patron Warrior does not have as many control tools against you as the Control warrior. You will definetly want to damage him as fast as possible. If you can not put in enough damage to get a kill even when patron hits, clear your own board by aggressively running your minions into his - especially when Emperor Thaurissan comes into play. You do not want him to run Grim Patron into creatures with less than 3 attack. Defender of Argus can provide you some protection if played on minions to create those taunts to get into the way of the patrons.

Control Warror:
Harder then Patron Warrior, as they have more armor and more control tools available. Try filling up your board early and don't hesitate to play Save Roar early to get the damage in, in hopes of finishing them off afterwards. Keep Innervate to play your late game cards early, but expect Dr. Boom to be taken out by Big Game Hunter. Keep silences for his Slude Belcher. Cross your fingers and pray. If this gets into very late game, you will have a really hard time.

General notes:

Taunt is key. You need to try and stop the hunter's minions and you can only reliable do that by taunting up your own. As Ironbeak Owl has been nerfed, it's mostly a one of - if even. 

Play around traps. You need to get a read on the type of hunter and what's currently played. Sometimes easier said then done. Throw down Nerubian Egg if you expect to run into an explosive trap. Every point of damage the hunter uses to get rid of one of your minions is damage not going to your face.

Lastly, every hunter plays Unleash the Hounds. If your board blows up too much, he will get great unleashes with Knife Juggler. Again one of the reason why Dragon Egg is a really great card for you, especially if taunted up.

Mulligan:
Keep Mark of the Wild[card]. If you are going second and don't have [card]Mark of the Wild, keep Defender of Argus, so you can coin him out on turn 3. The best 2 drop against a hunter is Haunted Creeper

Midrange Hunter:
Midrange is easier to deal with as the usual Midrange Hunter will try to control your board, which should be difficult for him. By the time Savannah Highmane comes out, you need to be prepared for a kill OR heavy damage to his face, forcing him to attack your minions instead of you.

Face Hunter:
Harder then the midrange hunter. If the face hunter draws both owls, it's really hard to win the game. Taunt up. Spawn minions. Beware the dogs. And good luck - often you dip low way too early.

General notes:

Much like Warrior, Rogue has weapon removal, which favors you. Try to clear his minions when you can, or at least kill tokens spawned by Violet Teacher (if they are running it). Keep dealing damage to the rogue to force him to try even harder to remove your minions and beware Fan of Knives

Mulligan:
Keep Nerubian Egg and Haunted Creeper. Do not bother to keep Dragon Egg unless you can buff it right away - the Rogue can easily deal with it with his weapon and dealing 2 damage to it with either Backstab or SI:7 Agent. Midgame playing one with Defender of Argus on top, this will be much stronger.

General notes:

Priest is one of the hardest matchups, as he can steal your low attack value minions and use them against you. If you can, buff minions attacks up to 4 to keep them (relatively) safe from the Priest's removal. Buffing up a minion (like a spawned nerubian) to 5 right BEFORE you play Dr. Boom or Cenarius is a good idea to bait out a Shadow Word: Death. Beware his turn 6 (or 5 if he has the coin) because of Cabal Shadow Priest. Try to buff your minions to three healths before turn 5 because of Holy Nova

Mulligan:
Keep Innervate in hopes of getting more power on the board quickly. Nerubian Egg is better than Haunted Creeper, especially if you can pop the egg at your leisure to get a 4/4 minion. It is not wrong to keep Savage Roar in hopes of zerging the priest down or to use it to get through a Deathlord

General notes:

If you're not playing freeze mage, the matchup against mage is quite good. Try not to pop your own deathrattles as your opponent will have an easier time removing your minions with his spells. Mages rarely run silence and most don't even run Sheep, which again is benificial for you. Taunt is still great to prevent the mage from going all face. Mages random effects like Flamecannon often work against him when facing you.

Mulligan:
Keep Nerubian Egg and Haunted Creeper. Dragon Egg is sometimes great to take tempo from the opponent as he will want to ping any 2/1 minions popping out with his hero power. If you're going second, keeping Swipe is an option to be able to remove Flamewaker.

Tempo Mage:
Best mage matchup. His Flamewaker will often shoot very blindly and trigger your minions. Still remove it whenever you have the chance so it will have no chance to snowball. Beware Archmage Antonidas and best have a way to deal with him. Keep Innervate if possible to get out Dr. Boom.

Mech Mage:
A bit harder matchup. Be careful his mechs don't snowball. Goblin Blastmage is thankfully rather inefficient against you. Fill up the board and taunt up. If you have 3-4 minions, play Save Roar early to put pressure on him, so his Fireball will target your minions instead of your face.

Freeze Mage:
Get lucky and pray he doesn't have his second Ice Block ready. Try putting damage in quickly and keep Keeper of the Grove against Doomsayer. If this drags on late game, it's unlikely you will be able to win.

General notes:

Unfortunately I have not played many Shamans currently. Try clearing all their totems whenever you can and burst him down with a good draw. Use Cult Master to draw and trade a bit more aggressivly then against other players. This will help you to outlast the Shaman.

Mulligan:
Keep Keeper of the Grove. Against Shamans I would consider holding Swipe in the opening hand to be able to deal with early game minions.

Aggro Shaman:
Just like with Hunter - Taunt is the key here. Especially in midgame, when Doomhammer can be expected. Try to remove Tunnel Trogg quickly, otherwise it's a bit of a race as to who can kill the opponent faster.

General notes:

Playing against a druid can be frustrating at times since they play a LOT of taunts. You need to get good Cult Master value to bash through your opponent's taunts. 

Mulligan:
Keep early game like Haunted Creeper and Echoing Ooze. Most druids need a few turns to ramp up. If they innervate out big taunts early and you cannot answer them you will lose. To be able to better answer them, keeping [card]Savage Roar[/card is generally a good idea IF you have early game to go with those cards.

General notes:

It's hard to put in general notes for Paladin, as the midrange version and the aggro version drift apart greatly and your playstyle will change. This however also makes it harder to mulligan. Prepare for the Paladin to Consecrate your board, either buffing your minions or putting unbuffed Nerubian Egg down so you will spawn the Nerubian.

Mulligan:
Paladin is the only class where I'm paranoid enough to keep a Swipe in the opening hand due to Muster for Battle. Asides from that, keep early game drops and Mark of the Wild

Aggro Paladin:
Better matchup - you need to stop the aggression. Put taunts up as good as you can and trade into his minions. Try to play your hand out, you do not want the Paladin to get good value from his Divine Favor.

Midrange Paladin:
Sounds weird, but my best matches against Paladin were won when I played a heavy board control game against them. The problem with zerging the Paladin down is that they will come back with heals. Try to remove his minions, always try to get Cult Master value, drawing 2-3 card to outlast them.

Control Paladin:
Pray that he didn't draw heals ... It will take the control paladin a bit to clear you board, but he will and then you're toast.

General notes:

Burst damage is key against the warlock. They will do a lot of the damage to themselves, use it to your advantage.

Mulligan:
Keep early game drops, especially eggs, and Keeper of the Grove if you can get it, who works great in both matchups.

Zoo Warlock:
The zoo warlock typically has the edge. Taunt up and try to spawn more minions then him. It's all about board control. Once the warlock starts tapping for additonal card, try to apply burst damage pressure to force him to deal with your minions. One of the biggest problems you will face is Mal'Ganis. If you can not deal with him, you have lost the game. I was sometimes able to set up a Savage Roar turn where I attacked his Void Caller and had enough power left to take out his big minion IF it comes down. Imp-losion sometimes works in your favor as you can run your Dragon Egg into the 1/1's to spawn more minions for yourself.

Handlock:
Build up a board, try to make it hard to remove. Do not taunt up Nerubian Egg, but instead the minions around it. It is too easy for the warlock to attack into the egg and then use Shadowflame to clear the Nerubian. Try not to get him too low too early, to avoid facing multiple Molten Giant. When going for burst, try to really kill him or the Moltens will come flying accompanied by an Antique Healbot. Taunt up so he has to run his big minions into your smaller ones. All in all, the sudden burst damage often kills the Handlock. Keep an Innervate handy to go into Combo on turn 7. The longer it lasts, the more it will favor the warlock.