Hearthpwn

First 5 matches with this deck => 100% win.

deck has no removal before turn 6, no activators for a turn 5 vilespine slayer, no board clears and no huge tempo cards before the quest, how are you supposed to take the board ever

Have you considered replacing Loot Hoarder with Novice Engineer for better tempo?
What do you think about synergy with deathrattle jades such as Jade Swarmer and Aya Blackpaw?

Backstabs are a necessity to Rouge's survival (as many others have said) and I see no point in waiting for the Sergeant Sally combo since she doesn't have charge. so I would put a threat like Edwin VanCleef, Arcane Giant or a Questing Adventurer since this could almost be a Miracle deck with the Caverns being an alternate Win Condition.

Lastly, Moroes is only good after the quest, he will fall to so many board clears and silences early on that he'll just be another dead card in the deck. I'd take him and maybe a few other cards out in exchange for three or four Pirates and Patches the Pirate

and by cost I mean name.

My bad, I was thinking of another card or two also released in the expansion. 

However, I still think that this is a rather slow quest to complete even with all of the bouncing and copying and such. One speed improvement would be to add Youthful Brewmasters in for more bouncing effects, otherwise this quest is kinda not worth it to me. Lastly, I'd put one or two Argent Squires and/or Stonetusk Boars for the really cheap 5/5 ability minions. 

Also, Edwin VanCleef is mostly useful BEFORE you play the quest reward, and Questing Adventurers are generally the same.

2* prep, 2* cold blood, 2* shadowstep (too many dead cards) and no backstab

This way you can face an untouchable board at even turn 4.     

The weakness of rogue is it is highly vulnerable, must be versatile to answer that. This deck seemed too dedicated for rogue to me.

I think that while the elementals make the quest much easier to activate, playing very poorly statted cards that do nothing since you don't have much synergy, on top of playing another 4 mana worth of do nothing cards, and then also spending 6 mana on the quest (1 for activation, 5 for spell) you will end up losing WAY too much tempo and without any board clears (other than sally, which isnt the most reliable) you will just get run over. I think adding vanish gives more than enough return effects to complete the quest, and then you can replace the rest of the cards with either removal (backstab, fan of knives), charge minions for burst, or draw (im not sold by this since bouncing alot makes your hand kinda clunky already, but a 2 mana 5/5 draw a card sounds dope)

Looks like a great deck, but my only problem with it is how are you going to survive with only two potential taunts and no heals?

no backstab.

0/10

-2 cold bloods +2 backstabs

-1 Sally +1 Edwin

Even after that, little taunt, no heal, no tempo, takes 8 turns to get going, no AOE(sally do not qualify as AOE), no finisher, and has minimum card draw. But has 4 Assassinate effects for some reason. Looking forward to playing this quest just one time if I get it from the pack and then proceed to dust it.

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Quote from McDazzlin >>

This deck looks fun! But also really terrible. Using the elemental seems like a bad idea, as the only real synergy they have is with the quest, and 1/2 elemental are not going to win you the game on their own. Basically if you dont draw caverns below your screwed, and that is going to happen in half your games. 

Unless you mulligan it

I would add tar creeper to this list. Not only helps to trigger stoneshaper's battlecry, it will also make aggro players weep. I would remove sgt. sally and N'zoth to accommodate the two cards. Also, the deck  needs more card draw. If you want to trigger the quest by using the 1/2 tokens, it has to be moreconsistent or else it will crumble against mid range decks. Nevertheless, I love the build.

Ill be testing this deck once the expansion is released, always liked nzoth rogue!

Crystal Core reward is 5 mana so is mimic pod tempo and combo activator

To start I want to say that I love this deck! Obviously, people have caught on to the synergy between firefly and the rogue quest, but I believe your list, on paper, has the best optimization of cards and numbers of cards in it.  Which is a problem for me, because it's air tight.  I'm having a hard to wrapping my head around playing rogue without backstab.  It's the staple early removal card, and combo enabler that other classes wish they had!  Whether it is right to include it or not has yet to be proven, but I cannot decide on what to replace it for.  I've considered subbing out cold blood for it, but then you ruin part of the sally synergy, that I think is great.  Now I'm thinking maybe given the low amount of typical rogue battlecry minions, SI-agent primarily, you could even go without shadowsteps.  This seems crazy to take out for the idea of the deck, but the more I look at it the more I convince myself the quest wouldn't be too difficult to complete without it.  It's a slower deck which doesn't need to be completed quickly when you have enough removal to back it up.  If you could tell me your thoughts I would love to theorycraft with you! :) 

 Edit: now I'm thinking the moroes is a "win-more" card and can be exchanged for 1 backstab.  I would still like to find room for another.

Your choices are justified, and it's hard to say what's better without seeing the meta! My logic is with envenom and slayers we may have enough hard removal for the larger minions including taunts.  In the list I run initially, I am going to replace mimic pods for fan of knives and moroes/ -1 taunt ele for +2 backstabs.  From there I'll look for any weak links to replace for SI-agents just because the value you can get with them and shadowstep/shadowcaster is bonkers.  We'll have to play it out to see!

-2 mimic pods, +2 fan of knives

-1 tol'vir stoneshaper, +1 backstab

-1 moroes, +1 backstab

It's going to be a blast tinkering around with this deck! It looks very promising the more I look at it!

I recommend not adding thistle tea! It is way too slow and sacrifices too much in favor of a gimmick.  The amount of 1/2 elementals you generate is enough as is imo.