Hearthpwn

Blizzard  will plant one Greybough in the Amazon forest for each Resurrect Priest defeated with this deck.

Not the best/easiest deck to play, long games (your win condition is literally a forest grown from scratch) thus it's not recommended for fast laddering. The % is there just because I don't care about percentages over small pool of games, nor I think the deck is truly optimized (still working on it, feel free to try and suggest any change).

Cheers lads!

Edit: Thank you for your support, I'm glad that you are finding the deck at least enjoyable! 

Introduction

This deck is a variant of the old Hadronox Druid that I decided to make after I found Greybough as my first legendary in the Darkmoon Fairie pack opening. I though this would have been only a meme and fun deck, but I found it to be more efficient than I initially thought.

The goal of the deck is to either outplay aggro with a lot of taunts, or to compete with control decks in the late value game. The plan is simple: play a lot of Taunt minions, let them die and resurrect them with N'Zoth, the Corruptor and multiple Hadronox (it can be resurrected by both N'Zoth, the Corruptor and Witching Hour).
Even though the plan of the deck is pretty straightforward, there are few things to keep in mind (depending on the opponent's deck mostly):

1) If you are facing a class with lots of Silence effects, you should use your resources wisely. This means that:
-You shouldn't be afraid to use your Archmage Vargoth to bait our one Silence, since it's not fundamental to your gameplan (and, most of the time, Priest and slower DH will silence it if they cannot kill it on the spot). If you are facing an aggressive deck, your opponent will mostly silence anything you play during the early game (e.g., Archspore Msshi'fn or Rotten Applebaum) so try to prevent Silence or transform effects when playing Greybough in that case.
-The main play of this deck is to drop lots of Taunts, then resurrecting them with Hadronox. You should always play Hadronox at turn 10, and then Naturalize it to fill again your board. This allows you to resurrect Hadronox again using Witching Hour lately in the game.
NB: When facing Mages with Polimorph, Shamans with Hex or any Hihglander deck with Zeph, remember that the token Sheep and Frog are BEASTS, so they can screw up your combo. If you cannot avoid transformation effects, try to kill your own Hadronox, resurrect him with N'Zoth, the Corruptor and kill it again (If you manage to, cube him) to increase your chance to resurrect him via Witching Hour.
-The strongest play of the deck is Witching Hour resurrecting Hadronox followed by Carnivorous Cube. This way you will create a strong board against most of the clears (the only exception being Psychic Scream, so try to play around that aiming to have a follow up plan - i.e., N'zoth in your hand).
-Archspore Msshi'fn is a 5 stars card in this deck. I'll be honest. when I opened him few months ago I was slightly disappointed, but I rapidly changed my mind: the versatility of this card is insane. It is a good anti-aggro tool, it can easily be a 2 for 1 if played early, and - due to its Deathrattle - adds tons of value to the late game if resurrected via both Hadronox or N'Zoth, the Corruptor. 
-Last, but not least, let's talk about our woody friend Greybough. With so many ways to resurrect him, this card is amazing: Just be sure to play him when you have at least one more minion on the board (obviously), and to be afraid to trade with him as much as you can. You should always aim to take advantage of his Deathrattle: e.g., you should trade with him first, then trade with the minion that gained his Deathrattle, so that you can trade again to keep Greybough rolling.  Also, cubing Greybough on an empty board and then using Naturalize on the Cube will give you 3 Greybough that requires basically six 6-Attack minions for a full clear (you can do this play at turn 9 or 10 using Lightning Bloom).

Final Notes: Even though the deck playstyle is kind of straightforward, the main difficulty is represented by the fact that you must constantly control your resurrecting pool to increase your best outcomes.
Against aggro decks, you probably won't play your full combo, and you should not be afraid to use Naturalize as a defensive tool more than your Combo enabler: so, you should play Greybough and let it stick as much as you can, so that you will resurrect him with N'zoth (maybe coupled with Rotten Applebaum). 
Against Control and slow deck, you want Archspore Msshi'fn in your resurrect pool as much as you can: with his Deathrattle you can compete in the value game in the late stages of the match, and you will delay fatigue significantly (and this might let you win on the long run). 

Card that I am testing now:

I was thinking to add Animated Broomstick to speed up trades with Greybough and Carnivorous Cube. I will keep you update!

As Jurke39 suggested, Terrorfiend Escapee can be an option if you are struggling against ress Priest!

I hope you have fun with this deck! Feel free to suggest any changes you are doing to this list, I eager to hear your inputs!

Cheers!