Hearthpwn

I crafted this deck to battle all the mech mages, mech paladins, demon hunters and druids on ladder. This deck (like most decks) performs poorly vs quest hunter but has a decent chance against everything else.

Mulligan:

Based on matchup but you'll generally want cards like Sacrificial Summoner, Full-Blown Evil and Mortal Coil in your starting hand.

You can cheat out your Imp Gang Boss from your deck if you end up with a two drop like Deeprun Engineer (which is a great value card for the mid game, the mech it provides is often invaluable) or recycle your imp to summon an early Gear Grubber. If the Grubber is in your hand it's not that big of a deal as it keeps discounting itself.

Late Game:

Naga Giant is optional, can be replaced with cards like Sea Giant, a second copy of Final Gasp or even with 2 copies of Escaped Manasaber to further boost your early and mid game and the consistency of your Sacrificial Summoner swing.

You'll generally want Ambassador Faelin and Gigafin your hand before you start throwing Altar of Fire at your opponent.

UPDATE:

Yeah, so the Summoner package didn't really work out, so I've swapped them for a copy of Rustrot Viper and Entitled Customer .