Hearthpwn

I am having a good time with this deck 25 - 9, right now. You should play like 2 turns ahead with all the secrets and multi effect cards. 
Mulligan - always look for Questing Explorer and Arcane Intellect in general. 
Against rogue, warlock, druid, paladin, shaman and hunter try to look for Arcane Flakmage, it can save your game.
Against Warrior, Mage and Priest go for the draw. 
It takes some games to understand how the deck really works.
First of all, don't worry about the mission! Yes, don't worry. It will happen eventually. Early game you should control the board with hero power and early minions. Your opponent will try to get rid of your minions as most of them have triggered effects. Don't play the secret after taking it from Ancient Mysteries unless you really have to. 0 mana secret works great with quest and Arcane Flakmage, for board control. Aggro decks will fill the board quickly trying to kill you early. As soon as you start playing secrets they will have to be more careful and try o play around it. 
Mid game you should be close to complete your quest, Dune Sculptor will give you a Mage minion everey spell you cast (including another copy of himself) and he will be a target as soon as he comes into play, make your opponent spend resources to get rid of it. You have Counterspell, Spellbender and Splitting Image to protect your minions. I've added only one Ethereal Arcanist as he is situational and you should play it when you have the board under control. Sometimes you will have to spend resources to be alive and will run out of cards in your hand, that's when I play Subject 9, even though it is situational as well, I've thought about changing it several times. Cloud Prince is an amazing card to deal with big minions or go face and Kalecgos is the one to close the game.
There are two terrible match ups for this deck, warrior and priest. Actually I've played against 4 priests and lost every game, 4 warriors (played against 6). 
I just felt like writting this because I've playing a different deck from the meta and I am enjoying it a lot.