Hearthpwn

Hey Demon Hunter! Swiggity swooty, I'm coming for your booty.
So apparently nobody appreciates the new guy, so I thought I might hit legend with a slower, more control oriented deck, you know - just for the hell of it.

And PedoPriest, Rogue, HippieDruid and warrior?
I taught those other "classes" what it feels like picking your teeth off the floor, with broken fingers. :)

Proof of legend:

Write-up

BuT yOu cAn nO LonGeR KilL DemOn HunTer'S WiN coNdiTioN aNd hEaL fOr 5 foR 0 mAna - dEcK sUCkS.

Ye, you're right, if your only idea of a good play is an instant win interaction against the most popular deck, go play something else. For everyone else? This is just another handlock deck with hyper-value cards and a 4 mana 5/4 that DRAWS YOU 3 CARDS FOR NO GOOD REASON.

This deck is basically an umbrella magic medicine (I'm not a doctor, don't quote me on that).

High stress due to low HP and a big minion giving you blood pressure? Mo'arg Artificer + Nether Breath cure that.

Erectile Dysfunction because you can't win a single game? Zephrys the Great, Dragonqueen Alexstrasza, Galakrond, the Wretched, and Kronx Dragonhoof give you a total of FOUR win conditions to change that.

Anxious due to all the aggro kicking your behind? Mortal Coil, Plague of Flames, Unstable Felbolt, Nether Breath and Dark Skies give you all the answers you need - while your own minions allow you to keep up somewhat in board presence.

One thing this deck can't cure is being a bitch, and you are free to quote me on that one.

How this deck seeks to win is by stabilizing against heavy aggro decks and winning by default after that, because your late game threats tower over anything they can throw out.

Against control decks you need to understand that your high minion count makes your play style closer to midrange than conditional control decks would have.

A huge difference between a good and a bad player piloting this deck is in how much value they can stretch out from their cards and 2-card combos, as well as which threats they will answer and when.

Replacements

While this deck isn't really budget friendly, I will go out of my way for the people only missing a card or two, and try to help you guys - keep in mind, I do not guarantee the deck being as good with these:

General

While all Galakronds are free, the deck is still playing a lot of legendaries and epics. The last legendary you want to craft for the deck is Alexstrasza. While she is high impact, I found her just clogging up my hand far more than any other leggy in here.

Win cons

If you're missing a big leggy, and have no big leggies that you think might serve the same purpose, you can try Evasive Drakonid. The card is insane in how many times it can win you a game on its own and I highly recommend it. He is also a dragon which is pretty big for your synergies.

Removal

I strongly believe that Hellfire is still a pretty good card, that can substitute 1 Dark Skies if you're an epic short.

Other

If you're just looking for other cards you can try out, or perhaps just have a few more expensive cards lying around: 
A second Mo'arg Artificer is solid in the deck, giving you a more consistent big heal and removal option. Sea Giant is another card that can be considered, leaning more heavily into a more traditional handlock classic. Acidic Swamp Ooze is also a great choice for a tech card that you will definitely find useful in this meta.

 

Mulligan

Generally, only ever keep Sacrificial Pact against hard aggro decks AND if you are on coin with an invoking card in hand.

Keep all of your removal against aggro and pretty much never keep any of it against control (except if the class in question has great early drops in control as well).

Always keep Dragonblight Cultist and Overconfident Orc.
Mo'arg Artificer is great with Mortal Coil and Nether Breath. 

If you can curve out decently with your invoking minions, keep that in mind as this deck uses its minions as another control tool against aggro, as well as pressure against control. Never keep any of your legendaries.

How Not to Suck

1. Aim to play Galakrond, the Wretched once he is fully invoked. This way you maximize value and improve your chance to win. Obviously, do not wait if playing the card is the only thing that can save you.  The weapon and the 4 demons are a large part of your winrate.
2. Wait with Kronx Dragonhoof. You will not want to play this card to draw Galakrond, the Wretched unless your next turn could be a huge swing and you are sure you don't need Kronx Dragonhoof to close out the game. While the 5 damage to the face lethal is big and often a finisher, consider the other options too. The buff option is huge if your 4 Galakrond demons + 2 demons from the hero power are alive.
3. Don't waste your removal at the first sight of a minion, especially against slow decks.
4. You will most often want to play 2 invoke cards ASAP, so you can draw off Veiled Worshipper. She gives you HUGE tempo. This step is often a decider in the mirror match and plenty other slow matchups. Keep an eye on your hand limit. You don't want to risk to overdraw in this deck, especially before you've seen your win cons.
5. Hold on to your Sacrificial Pact for when the time is ripe. Try to sac your imps when they would either die for certain, get eaten in crappy trades or when you have large boards smiling and ready to eat one of Priest's many mass removals. Imp face damage adds up and trading is another source of removal.
6. Using a deck tracker is a good idea (even though I did not use one in my climb). It is a very useful tool to track dragon synergies, as well as how much removal, heal and minion threats you have left in your deck. 
7. Plague of Flames combos with invoke cards.
8. Mo'arg Artificer combos with Dark Skies, Mortal Coil, Unstable Felbolt, and most importantly,  Nether Breath.
9. Don't just crap out a handful of minions on the board against heavy control decks. Priest will just eat them all and thank you for the free win. Save up your minions.
10. On the topic of saving things, think before playing every card. Does playing the card truly put you in a position better than before playing it? Card advantage, tempo, board advantage, health totals and the hand limit are all factors.
11. Don't overcrap the tap. If you run into fatigue every game vs control and tap 12 life every game against aggro, you do indeed overcrap the tap. Chill with the hero power and check tip number 10.
12. Don't undercrap the tap. Warlock has the most powerful, but also the most skill-based hero power. Mastering its use is a big factor in getting good at warlock decks in general.
13. Learn. While there is a metric shitton of luck in Hearthstone, that doesn't excuse you and give you a free pass to be bad. After every loss or losing streak ask yourself: "Am I doing something even slightly wrong?", then when you start to see the answer yes, start to ask yourself the same thing WHEN YOU WIN. Winning won't mean you are the better player 100% of the time. Stay humble. Every single missplay you recognize is a missplay you will not repeat.
14. If they're playing Priest say "Thank you." when you win.  Stay nice and respectful to your opponents. Unless they are playing Priest.

HUGE SHOUTOUT TO SHENNON FOR HELPING ME WRITE THIS SECTION!

100 upvotes - coaching session for 5 random newer players

If we reach any higher milestones, suggest your own rewards.