Hearthpwn

Wow - I couldn't believe it ... FIRST TRY!

I got my Deathlord to 64 attack / 64 hp either on turn 9 or 10, can't remember.

I was actually able to get a Lightwell out on turn 2, and a Deathlord on turn 3. Managed to keep them alive and buffed up through turns 3 - 7.

I drew two Mind Control Techs on turn 4 and 6 I believe it was, allowing me to easily deal with the bone constructs. 

AMAZING deck. I wouldn't bother trying any other deck for Heroic Nefarian. Nice work!

/edit Yes, RNG was a bit on my side. That being said though I had multiple ways to deal with minions and just based off the fight and the cards I had in deck, I know that this deck is 100% doable. Assuming the RNG gods hate you, I can't imagine this deck taking more than 5-10 trys at worst case scenario. GG.

/edit2 For those of you doubting me. I used divine spirit twice on top of a Velen's Chosen,  Dark Cultist deathrattle'd, and Power Word Shield'ed Deathlord. Not in that order though, my divine spirits were spaced out as I believe divine spirit was one of my mulligans if I remember correctly. Yeah ... I had a perfect mulligan and great draws, ha.

First try!

I managed to ramp up a Frothing Berserker to 18 attack in one turn by combo'ing Cruel Taskmaster + a bunch of Grim patrons & Revenge combo.

IF YOU'VE BEEN STRUGGLING WITH THIS BOSS, LOOK NO FURTHER, THIS IS THE DECK.

I'VE Created an account just to let everyone know THIS is the guide you should use, and none other.

After trying 8+ decks and 80+ games over 3 days, this was the guide that led me to victory. Please be sure to see comments and original strategy this guide was inspired by ( http://www.hearthhead.com/decks/0-cost-hr-nefarius-destroyer ) as it could provide some insight.

NOTE: You could potentially sub in mass removal cards like Bouncing Blades or Brawl, I had a few attempts with this deck where I almost won, some followed the exact cards in this guide, some added a few cards like Bouncing Blades/Brawl. Ultimately, on my 6th attempt, I downed this heroic bastard using the exact cards listed in this guide. Not that I think this guides exact cards are essential, small variations are certainly doable. The idea though is spot on, and most these cards listed here, if not all, are good.

THE KEY really is just clearing minions early as best as you can, trying to leave nothing up, and NEVER leaving your own minions up. NEVER EVER. A common mistake I was making was I would hesitate on attacking a minion with one or two of mine in combination with spells, because I felt like I was trading too many cards just to kill one guy. BUT THAT IS OK, BECAUSE YOU ONLY NEED TO CLEAR MINIONS OFF BOARD UP UNTIL TURN 6 or 7'ish. After that, it's just a fatigue waiting game! You'll find yourself using very inefficient combinations of minions and spells just to take down one minion, and it feels dumb, but note that IT'S NOT. If it means you kill a minion, then you are one step closer to leaving none up on the board, and that's good.

The most important thing = never leaving your minions up, because it frees him up to use cards, and once he's free to use cards, he no longer goes into fatigue mode where he just instantly ends turns and plays no cards. But if you've managed to clear all minions and survive past turn 5/6/7'ish, he essentially just ends the turn instantly every round while you just armor up and wait for weapons. Once you have kill potential, you can throw down your charge minions.

One quirky thing I had to do was to try to spend mana and somehow use non essential cards as best as I could while I waited for Weapons to come into my hand, during the stabilized/fatigue stage. (THIS DOESN'T MEAN USING MANA TO DROP MINIONS, I'M REFERRING TO SPELLS). Since I had 10 cards in my hand I wanted to make sure I wouldn't burn the essential Weapons I wanted to get out of my deck.

Good luck out there.