Hearthpwn

Always keep: Flame Imp, Voidwalker, Dire Wolf Alpha, Haunted Creeper & Knife Juggler. (some people like to always keep Imp Gang Boss too, its up to you, vs warrior this can be nice because its good vs Fiery War Axe.)

If you have coin you can keep Nerubian Egg + Abusive Sergeant & Imp Gang Boss.

Keep Mortal Coil vs hunter and paladin because there is a good chance you'll be able to use it verry fast and need it to slow down fast aggro/face decks.

Keep Abusive Sergeant  if you can't keep any of your other cards (to ensure you can play something early even if you have to lose the +2dmg) in some other situations you might also want to keep it. By example if you already have a Voidwalker and Haunted Creeper so you can play cards for two turns already and you will likely be able to buff them for a good trade quickly. Besides that i also like to keep Abusive Sergeant vs hunters because you might need the extra 1 mana body to trade vs early face hunter threats to slow him down.

Warlock: When you are vs a warlock it is most likely zoolock, handlock or malygoslock. When the game starts just play like normal but try to figure out what kind of warlock you are against asap. If its a zoolock try to gain board control and dont be afraid to extend your board since they normally never run board clears, because of this spells like Imp-losion will be verry strong here.

If it is a handlock try to inflict as much dmg face as fast as you can (watch out for board clears, dont overextend) you might want to pause face a little above 10 health to avoid one or two free Molten Giant so that you can finish him the next turn. Its also verry tempting to silence Twilight Drake but consider that you might want to save it for when he gives taunt to a 8/8 giant.

When its likely a malygoslock you also want to kill him as fast as possible and watch out for boardclears.

Warrior: When you come vs a warrior its most likely a patron or controll warrior. I've seen some aggro and mech warriors but they are verry rare.

Patron warrior is usually a hard matchup. The best thing to do is to rush face as much as you can and make try to avoid him from drawing to manny cards (by example hitting Acolyte of Pain for 3 damage before he can kill it with 3x 1 damage or leaving manny damaged minions on the board for Battle Rage) when you reach mid/late game or he just played Emperor Thaurissan and he might start his combo try to get rid of 1 attack minions so he'll get less value out of trading with Grim Patron. Also watch out with life tap since they can reach alot of damage in 1 turn.

Control warrior is a bit easier. Once again try to rush him down and watch out for weapons he could play. When you reach mid or late game he will most likely stack alot of armor and win the game so make sure he's dead before that stage of the game.

VS Druid, When you're facing a druid it is likely a combo, ramp or perhaps even aggro druid. At the early stage of the game watch out for Wrath, Keeper of the Grove & Swipe. You can bait one of these on your Flame Imp so you can play a Knife Juggler the next turn for example. Try to keep alot of pressure on his face and always try to count if he can kill you with a combo (Savage Roar + Force of Nature), avoid this possible lethal with taunts/clearing board. Make sure to use your Ironbeak Owl wise, for example on a Ancient of War. And always keep Innervate in mind.

Hunter: So when we have hunter there are face hunters, hybrid hunters and midrange hunters. When you dont know what hunter he is act as if it is a face hunter, voidwalker and mortal coil will have a lot off value here to trade with the leper gnomes, worgen infiltrators etc. Feel free to use your owl on a mad scientist if you have too. You want to have board control as early as you can yet don't overextend for unleash the haunts and explosive trap. Try to stay out of lethal range with board clearing and taunts and if its safe enough rush him down.

(Other matchups are under construction.)