I'm not a pro or semi-pro or anything, just having some good luck with this deck, thought I'd throw it out there.
Some notes worth mentioning:
Crazed Alchemist serves a few purposes. First, convert Humongous Razorleaf into an 8/4 after Silence or Purify. The 8/4 clears out big threats and if you can double up its health, you've got a 16/4! Nice. It also kills annoying stuff like Public Defender, pesky totems, and so forth. In a pinch, you can swap Northshire Cleric into a 3/1 to clear out a 3 body. It's a more versatile card that it seems like, but you can probably get away with one.
Doomsayer is for tempo.
Including both Silence and Purify is just card draw engine. These plus Gadgetzan Auctioneer keep the deck cycling. Try to save Purify for the Humongous Razorleaf if you can. A nice one-turn combo is Gadgetzan Auctioneer, Humongous Razorleaf, Purify (draw 2 cards). Gets you a 4/4 and a 4/8 on the board and cycles the deck.
Watch for opportunities with Radiant Elemental in your mulligan. Remember this lowers spell cost by one. Especially if you are going second. I've coined out Radiant Elemental then played the 0-mana Power Word: Shield on it, then a 1-mana Inner Fire to get a 5/5 on turn 1!
I'm not sure what's best for mulligan yet but I generally go for Northshire Cleric, Radiant Elemental, Power Word: Shield, and Inner Fire. You can get some big, fast minions out. I've had 8/8 Northshire Cleric on turn 2 before.
I have Dragonfire Potion because your finish is usually going to be Humongous Razorleaf and the 4/8 body can survive Dragonfire Potion. The +3 damage over Holy Nova kills quest Rogue minions and leaves your big guns alone. It's a little slow but if Quest Rogue finishes before you can play Dragonfire Potion, you're losing anyway.
I've toyed with 2xMass Dispel. It shuts down Quest Rogue minions, clears taunts and (I think) Adapts, draws cards, it's just all helpful.
Again: I AM NOT A GOOD PLAYER. I've never broken rank 10. This deck WILL NOT take you to Legend. Or, if it does, it's beause you're good, not because the deck is good. Hopefully somebody smarter than me can make this deck better. Welcome any suggestions.