Think of the deck as a handlock without giants. You want to tap a lot for extra cards and make good tempo plays with your combos to catch up. The general idea is to fight heavily for board control, heal up, tap for even more cards and burst down the opponent with your buffs. If the game goes into fatigue, INFERNO might save you.
You definetely want to mulligan agressively for the small combo and Mortal Coil. Hellfire [/card] is not very good here because of all the deathrattle minions. If you happen to start with a [card]Voidcaller and Mal'Ganis, you can risk keeping it, because the hunter might be forced to trade his entire board into him. Avoid tapping in the midgame unless you need a very specific topdeck (like a Healbot) badly.
vs mech mage
Again, you should go for the small combo, however, Hellfire is a lot better, because it combat the opponent's minions better. You can keep the big combo in the opening hand if you want to, but don't be surprised if you get rushed down.
Throw away your Mortals coils and small buff cards. The best cards against Drud are Nerubian Egg and Hellfire. If you get those, you can hard counter their standard opening with Shade of Naxxramas. Other than that go for the big combo.
vs priest and control warrior
Keep the small combo if you have it in hand, but otherwise go for the big combo. Keep tech cards like Big Game Hunter vs Warrior. Do not let Jaraxxus get summoned without the battlecry, because you might need those Infernals. Do not let their Sylvanas get one of your big demons.