Hearthpwn

This is a March of the Lich King iteration of Mecha'thun rogue. It is similar to older lists, only I've excluded some outdated cards (see below) and included some of the cards from the latest expansions. Overall, it is not the best deck for climbing but you'll be surprised at how fun and surprisingly consistent the turn 6/7 OTK can be. With practice, you can easily get a winrate above 50%, I'm currently sitting at 56% in dumpster legend.

How the deck works

The deck has 5 key combo pieces: Mecha'thun, Anka, the Buried, Myra's Unstable Element, Secret Passage and Animated Broomstick/ Wild Pyromancer. Preparation and/or Counterfeit Coin are also great to have.

The aim of the deck is to use Anka, the Buried to discount Mecha'thun while in hand, ideally on turn 5. There are a few possible plays that can be done afterwards depending on which cards you have in hand.

The most basic combos are the following:

(8 mana) Mecha'thun(1) -> Broomstick -> Myra's Unstable Element -> Kill broomstick -> Secret Passage -> Kill Mecha'thun

This combo only needs the 5 combo pieces mentioned above but is also the slowest at 8 mana. It also relies upon the enemy having minions into which you can trade your Mecha'thun.

(5 mana) Coin -> Prep -> Mecha'thun(1) -> Broomstick -> Myra's Unstable Element(3) -> Kill broomstick -> Secret Passage -> Kill Mecha'thun

This is the ideal combo, requiring only 5 mana but also needing to have coin and prep. Although it seems harder to pull off, the truth is that it's not uncommon to have coin or prep in hand on turn 6. Again, this can only be done if the opponent has minions into which you can trade your Mecha'thun. Variations can be done with only prep or only coin.

(9 mana) Wild Pyromancer -> Myra's Unstable Element -> Mecha'thun(1) -> Secret Passage

This is for when your opponent doesn't have minions into which you can trade. Can be combo'd with coin and prep to decrease cost to 6 mana. Credit to user Spiderhaz, whose guide (https://www.hearthpwn.com/decks/1416089-castle-nathria-mechathun-rogue) inspired me to add the Wild Pyromancer.

Mulligan

You want to always keep Shroud of Concealment and Secret Passage. Keep Swindle if you start with coin.

After that, any card draw, including Cavern Shinyfinder.

Anything else is sub-optimal in my experience. I would not keep combo pieces.

Card selection

I have chosen to include one copy of Ghostly Strike. It provides decent card draw and helps clear some aggro pieces, notably Filletfighter.

The two copies of Door of Shadows can easily be replaced by another Ghostly Strike or Shadow of Demise, but I find that door is much better for tutoring shroud and swindle.

I've completely excluded Cloak of Shadows, as I find it to be terribly inefficient at 4 mana.

Helpful tips

Make sure you don't use both copies of Secret Passage for card draw, as this would virtually always result in a loss.

Remember, your board needs to be empty for Mecha'thun deathrattle to work. Make sure that your Anka, the Buried is dead before you combo. That said, the opponent will usually take care of that for you.

Don't forget that Myra's Unstable Element will draw, not necessarily mill, your deck. If you are missing a combo piece, especially passage, you can often draw it using Myra's during your combo.

Blackwater Cutlass can be used to discount your combo pieces and it often does. Keep an eye out for the cost of Myra's Unstable Element and Secret Passage. Remember that Cavern Shinyfinder will always tutor cutlass.

Don't be afraid to use Auctioneer Jaxon for card draw if you have one tradeable card in hand. She is best used at 4 mana, where you can get 2 chances to discover ideally shroud, swindle or a combo piece you need.

If you are using Wild Pyromancer in your combo, make sure you coin and prep in that order BEFORE playing the pyromancer, as you can only cast 2 spells (Myra's and passage) once the pyromancer is on board.

Matchups

Bad matchups: This deck is not the best into aggro matchups. Pirate rogue and even shaman are likely to give you a bad time, as games often close by turn 5/6, which is when your deck comes online. That said, I have won a few games into these decks so it's not a guaranteed loss.

Even matchups: Maybe I'm overestimating the deck or my experience is biased, but secret mage appears to be a pretty even matchup. It is usually slower than other aggro decks and you can use Jaxon and Wild Pyromancer to remove Objection! before going for your combo.

Decent matchups: Res priest is a really good matchup since it doesn't run much disruption and it comes online around the same time as this deck does. Same goes for control decks, but watch out for Mutanus the Devourer, Theotar, the Mad Duke and Dirty Rat. Despite these cards being common in control decks, a lot of the more reactive control decks will be taken by surprise by the deck you are running.

Conclusion

An awfully long guide for a deck that is more for fun than for climbing but I've just enjoyed running this list so much. As I mentioned in the introduction, after you get used to the deck, you will be surprised by the consistency of the turn 6/7 OTK. And, while aggro decks can be very frustrating, the satisfaction of pulling off this combo is, for me at least, more than enough to make up for it.