Hearthpwn

Tech Cards: This variation of zoolock would run two copies of Defender of Argus and two Skelemancers one Abyssal Enforcer and one Fellfire Potion, but the thing is that the the huge tempo you will probably get protects you from getting overpowered by aggressive decks, and the problem with AoE removal isn't that big at the moment so you can afford having a vulnerable board. However you can experiment with those cards, with any cards actually, just don't go for the pirate/Bloodreaver Gul'Dan packages, those two come with a huge draw back each while this deck is better off without the bad demons that the DK resummons and without the vulnerability to Golakka Crawler and more draw RNG. 

Mulligan: You pretty much want many 1 drops, however you always keep Keleseth and even coin him as you want tempo and playing him on 2 is weaker than taping or playing a Flame Imp or two other two drops and the 2/2 body on 2 is good to trade with, you also keep Earthen Ring guy with Happy Ghoul as you hope to get 3 mana 9/9 on 3/ 2 with the coin :)) just don't be too greedy

Playstyle: depending on your opponent you either go for tempo, keeping yourself alive or just playing around the crap priest runs, the hardest matchup is priest, and one of the reasons I run Mindbreaker I made this deck last night and played from rank 19 2 stars to rank 14 3 stars, only lost 3 times 2 times against priest at rank 15-14 and once against a pirate warrior who drew perfectly while I had my 5-7 drops in my starting hand, I pretty much faced net decks, much aggro, I got to say it, this decks wipes all aggro decks out, while against priest I defeated 1 highlander priest and 2 DK priests, not many priests last night, I'll play some more and guide you in the comments if this deck gets any attention, tho I'm  very busy this weekend and the fallowing week as well