Hearthpwn

Reasoning behind some card choices and disuse of others
Even with a Stargazer Luna i wouldn't go with it, between 6 cards that tutor/play your secrets, Aluneth and double Dublicate i find that I have enough fuel and draw in most games (8/10 games).

Why Forgotten Torch and where is Polymorph: Boar?
I prefer Forgotten Torch over Polymorph: Boar, as it is better at dealing with small minions in the early game(where the deck is most potent) and often close out more games for me when it comes back as Roaring Torch. Forgotten Torch seems to serve the same purpose as Polymorph: Boar and in my cases has performed better.

Single or Double Flame Ward?
I tried running 2 Flame Wards, but in most games the second one just sat in my hand the whole game, as Arcane Flakmage and one copy cleared more then enough in most games.

Ice Block
I find that Ice Block rarely works, as games where it is popped I would lose anyway or it would take up a slot for a good secret, and is really only useful as a way to keep Cloud Prince or Medivh's Valet active when you have no other secrets, which is rare. The ONLY rare case where I have seen Ice Block being game winning is in mirror match ups, that kept going into the late game where i had enough to kill my opponent and Ice Block prevented that, and he miraculously had the cards t kill me the turn after, all other match ups Ice Block seems to be mostly useless.

Other Minions With Secret synergy
I (as well as the winrate) find that Ethereal Arcanist is too slow to put in the deck, even though it seems tempting at first, as well as all other cards that has a battlecry that does ANYTHING with secrets and Secretkeeper. The only one that is interesting to theorycraft with is Masked Contender, who seems to perform fairly good, but is still outperformed by all other minions in the deck, and it is hard to find a spot or need for him.

As always, find what works best for you and try to experiment, even with some options that i didn't include in my deck or specified that I wouldn't use.

Playstyle / Guide
Play the deck as an aggressive miracle deck and shuffle through it as fast as possible, only/mainly go face with your direct damage cards like: Cloud Prince, Medivh's Valet, Roaring Torch and Fireball. Prioritize getting Duplicate to activate on Cloud Prince or Medivh's Valet, or as a secondary priority Kabal Crystal Runner. Use tutor cards like Arcanologist, Mad Scientist and Ancient Mysteries to thin out your deck and cycle faster, this ensures that your top decks and Aluneth draws are better, since it's generally not good to draw secrets, caus it slows down the deck and make it take longer to dig down to your smorc cards, e.g. Cloud Prince, Medivh's Valet, Roaring Torch or Fireball. When nearing fatigue it's a good idea to keep at least one secret that can be hard to activate for your opponent in hand, to ensure that you always can activate your Cloud Princes and Medivh's Valets, or to play around this by playing them early and keeping Roaring Torch and Fireball instead.

How to use Explosive Runes and Potion of Polymorph
Try getting Explosive Runes to activate in the early game on low health minions, since it kills the opponents hero faster, and instead/later try to use Potion of Polymorph when you think your opponent is about to play a big/important minion. I felt like pointing this out as it might not seem obvious and i see a lot of players using Explosive Runes as a control tool, which i have not found a lot of success with. Of course once your past early game you can merely use it as a way to keep board control and minions off the board.

Mulligan Guide
Try to get cheap minions like Arcanologist, Mad Scientist, Kabal Lackey and Medivh's Valet(for smorc, maybe control). Cloud Prince is insanely nice to keep in your opening hand, he presents a nice body that is hard to contest and pushes 6 damage face, ON TURN 5, do try to keep him in your opening hand, especially since he becomes hard to play with Aluneth's drawing with a 5 mana cost, while you also have to play other cards. When considering secrets you should try to get Flame Ward, if you are afraid that your opponent is gonna go wide/aggro/zoo, and try to keep Explosive Runes if u can, to get some early, high smorc and control. Thirdly i would consider to keep Kirin Tor Mage or Arcane Flakmage for a strong turn 3 against certain matchups(e.g. you have Flame Ward and Kabal Lackey and are against aggro), also consider keeping Duplicate if u already have Medivh's Valet and or Kabal Crystal Runner as it is a really strong combination. In general look for Aluneth, a few cheap minions, ways/cards to cheap out and play Kabal Crystal Runner, smorc Runes, early board clear options and lastly  match up dependent secrets, like Potion of Polymorph against Warlock or Counterspell if you are going second.

Mulligan Guide (almost) always must keeps:
(almost) ALWAYS keep Aluneth(highest drawn-,  highest played- and almost kept winrate during mulligan). Despite Kabal Crystal Runner low kept rate during the mulligan, it has one of the highest winrates if kept (just consider match ups and your other cards before keeping), even with just one card like Kabal Lackey that discounts secrets or none, i still keep this card, always, the deck gains amazing winrate % when it is kept. Try to keep Cloud Prince, a nice body that is hard to contest on turn 5 with 6 damage going face, makes it one of the best keeps.

Go smorc