Hearthpwn

simple way to beat him is  w8 him to play millhouse and then 1 shot him as druid simple blood magic brawl deck works

Heroic High Justice Grimstone / Dark Iron Arena Boss ungoro Freeze Mage Deck by Zelgraz - Apr 30, 2017 View Deck String Export to BBCode Export to Cockatrice Export to MarkDown Export to Html Clone this deck
Minion (10) 1x Alexstrasza 1x Bloodmage Thalnos 2x Doomsayer 1x Animated Armor 2x Mind Control Tech 2x Mad Scientist 1x Medivh's Valet	Ability (20) 2x Flamestrike 1x Ice Block 1x Pyroblast 2x Blizzard 2x Molten Reflection 2x Ice Lance 2x Arcane Intellect 2x Forgotten Torch 2x Mirror Entity 2x Frost Nova 2x Frostbolt
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Heroic BRM vs Dark Iron Arena Unknown Deck by LordTrashman - Oct 22, 2016 View Deck String Export to BBCode Export to Cockatrice Export to MarkDown Export to Html Clone this deck
Minion (16) 1x Sylvanas Windrunner 1x Tirion Fordring 2x Aldor Peacekeeper 2x Knife Juggler 1x Mind Control Tech 2x Wild Pyromancer 1x Annoy-o-Tron 2x Cult Apothecary 2x Tentacle of N'Zoth 2x Youthful Brewmaster	Ability (14) 1x Enter the Coliseum 2x Divine Favor 2x Equality 2x Muster for Battle 1x Repentance 2x Consecration 2x Sacred Trial 2x Humility
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It's almost a Secret Hunter deck Secrets Hunter Deck by setatakahashi - Sep 18, 2016 View Deck String Export to BBCode Export to Cockatrice Export to MarkDown Export to Html Clone this deck
Minion (15) 1x Barnes 1x Ragnaros the Firelord 1x The Curator 2x Savannah Highmane 2x Secretkeeper 2x Cloaked Huntress 2x Kindly Grandmother 2x King's Elekk 2x Houndmaster	Ability (13) 2x Call of the Wild 2x Snake Trap 2x Snipe 2x Animal Companion 1x Explosive Trap 2x Freezing Trap 2x Kill Command	Weapon (2) 2x Eaglehorn Bow
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One of the hardest bosses ever. I only beat it because he gave me the victory. After 50-60 tries with Mage (mind control tech, bran , mirror entity) i have lethal 8 damage minion, he has 8 i have 2 life. He plays  a legendary and converts mat pagle to 1 1 chicken, + 1 1 token and i am dead next turn. for some reason he did not attack with the chicken. gg

This is, for a fact, the best deck to beat this boss with!

http://www.hearthpwn.com/decks/260214-extremely-easy-slow-but-always-reliable-dark-iron

Humility - Lorewalker Cho Paladin!!!

He also has Al'Akir the Windlord and Sneed's Old Shredder in his deck.

and Vol'jin 

Heroic Dark Iron Arena Basic Mage Unknown Deck by DarkJak - Apr 3, 2015 View Deck String Export to BBCode Export to Cockatrice Export to MarkDown Export to Html Clone this deck
Minion (18) 2x Deathlord 2x Sludge Belcher 2x Elven Archer 2x Sen'jin Shieldmasta 2x Voodoo Doctor 2x Frostwolf Grunt 2x Goldshire Footman 2x Ironforge Rifleman 2x Silverback Patriarch	Ability (12) 2x Arcane Intellect 2x Fireball 2x Frost Nova 2x Frostbolt 2x Mirror Image 2x Polymorph
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Basic Deck made using Kripparian's Lorewalker Cho + Frost Nova Chain

There's always this possibility... Trial and error and a "bit" inconsistent. But oh man... It is fun when it works! :)

 

Did H Arena with plain old Handlock. H Thaurissan I did with a priest deck with one Mad Alchemist, I didn't even think to use Lightwell(I de'd the ones I used for naxx) but I was lucky enough to get one from a shredder, which I buffed up to win with. I don't remember what I beat GG with, probably a retarded amount of big minions. 

Here is the deck with which I had had success beating second boss on heroic mode. VOD inside.

Aspard's Dark Iron Arena (Heroic) Unknown Deck by Aspard - Apr 3, 2015 View Deck String Export to BBCode Export to Cockatrice Export to MarkDown Export to Html Clone this deck
Minion (17) 1x Emperor Thaurissan 2x Big Game Hunter 2x Cabal Shadow Priest 2x Recombobulator 2x Mind Control Tech 2x Sludge Belcher 2x Wild Pyromancer 2x Northshire Cleric 2x Shrinkmeister	Ability (13) 1x Mindgames 2x Holy Fire 2x Shadow Madness 2x Silence 2x Holy Nova 2x Shadow Word: Death 2x Power Word: Shield
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This fight was very punishing cause of nozdomu who cost me a game the win as a priest so I went back with a druid and rocked it. http://www.hearthpwn.com/decks/220454-heroic-dark-iron-arena Mind you I was planning on exploiting naturalize while cho was out he didnt drop till late game so I have to work it but the taunts really helped.

I just knocked this guy out using a priest deck similar to the one suggested. 

 

Here's my list

Circle of Healing x2

Mind Vision x2

Power Word: Shield x2

Northshire Cleric x2

Resurrect x2

Shadow Word: Pain x2

Doomsayer x1

Shadow Word: Death x2

Thoughtsteal x2

Alarm-o-Bot x2

Big Game Hunter x2

Mind Control Tech x2

Mindgames x2

Auchenai Soulpriest x1

Holy Nova x1

Vol'jin 

Lightbomb x1

Mind Control x1

 

Basically, he played a millhouse manastorm, i mind controlled him, played some thoughtsteals and mind visions, got my alarm-o-bot early, quit using him once i drew a bgh. Used doomsayer early, gg

I beat this boss in spectacular fashion with a wombo combo Paladin Deck.  Mulligan for lay on hands and either a 1 or 2 drop, preferably echoing ooze.  Then wait for him to play Millhouse Manastorm and cycle your deck for insane results.  An alternate win condition is to get lucky with Mind Control Tech and stealing something like Hogger which the AI can't deal with easily due to not having spells.  It may be necessary to stall with board clears like Equality/Consecrate or Wild Pyromancer/Consecrate to set up a later combo when the AI plays Millhouse.

Tried a variation of this (didn't have a few of the cards) and won after a few tries.  It really is just waiting until he's stupid enough to play millhouse then cycling through your whole deck for free until you find ooze and then buffing it with blessing of kings, blessed champion and blessing of might.  Fun deck :)

I registered to thank you for this list. This got me the win in three tries after countless attempts as Freeze Mage.

For others trying: HARD MULL for Lay on Hands and reset if he doesn't play Millhouse first. There are obviously other conditions to win but IMO it's more worth your time to reset.

Fun cheese!

Worked for me too, with a minor variation since I didn't have some of the cards.  

-1 MCT
-1 Blessed Champion
+1 Avenging Wrath
+1 Blessing of Wisdom

I didn't have Avenging Wrath but I agree it's worth including, ideally the deck would probably include 2, and drop a MCT and/or a shielded minibot

Beat him on heroic easily with Rogue: Betrayal, AoE, Vanish, MCT, and Alarm o Bots.