Hearthpwn

Why not Headmaster Kel'Thuzad ?

Headmaster certainly is a card you could put in over one of the cards I mentioned earlier in my comments which you can take out for personal preference. The reason why I don't like Headmaster myself, is because its main synergy lies with cascading disaster, which is very late game because you want to corrupt it first, and you need to wait until at least turn 8 to use both cards in one turn. Versus some aggro boards and let's say allura coin tip the scales full murloc board, turn 8 is too slow and destroying 3 random minions and summoning 3 random ones just doesn't make the cut for me personally. I'd rather have more removal, I already think cascading is good enough without the Headmaster and I don't really like playing Headmaster as a tempo play and hoping I get cascading synergy the turn after because that just seems too wishful to me. It can certainly have its moments and I can understand some people putting him in because they just like the flavor or want the deck to be more expensive. But from the experience I have with this deck, there are better ways to build boards with this deck and the effect Headmaster has with this deck is just not defining or game changing enough.

I think Headmaster is mainly a slow situational greedy card you keep in your hand most of the time and wait to play the right moment, and in my opinion the deck is already saturated in that category, this deck thrives in the late game. The main problem this deck has is surviving and being able to reach the late game, and I don't think Headmaster solves that problem. (I must admit, if you happen to face a slow control deck and you chose to put in Headmaster, yes it can be really impactful and seem like a good card, but you must consider if his effect is really that unique and whether or not it wins you the game in that particular case, when without Headmaster you might have won that particular matchup anyways and Headmaster did not really change anything in that case). 

I've experimented with taking out c'thuun and valdris and putting in 2 hysterias. C'thuun is NOT missed at all in this deck, it performs way better without so deffo take out c'thuun for this card if you want your deck to be more viable. Valdris contrary to what I expected turned out to be missed, yeah you can still get it from twisted knowledge, but that's not guaranteed. I admit valdris may not be as important as I am trying to make everyone believe he is, but he has stolen my heart and after some matches I took out one spirit jailor and I put valdris back in. I guess the cards in this deck which are switchable to personal preference are the jailors, luckysoul hoarders, c'thuun, harrison jones and valdris. I recommend experimenting with these cards and try find what suits you best. As for the other cards in the deck, in my opinion they are pretty much stapled and too important and you shouldn't change those. The biggest counters to this deck are miracle otk mozaki mage (nothing you can really do honestly, like what, twisted knowledge into a chaos gazer and hope you exactly hit a crucial card? Turbo out Tickatus really quickly and try burn crucial cards before they draw them? Even though they draw their whole deck somewhere around turn 5-7?) and OTK demon hunter heavily counters this deck, but at least you have time to try and get to play tickatus and hope for a lucky Il ginoth burn and it is not an auto concede and you do at least have a chance. This deck performs best versus other slow decks like paladin, warrior, highlander mage, any priest deck, just any slow control based matchup really. As for aggro decks... it depends... Arbor druid it completely shits on and you win almost all the time because you just have wayyyyyyy too much efficient board clears, but face decks like the stealth rogue and bomb warrior which are more weapon oriented I have to admit the deck kind of struggles with. Those matches aren't auto concede matches though you should play them out and you do stand a reasonable chance to win against them. Just not mozaki otk mage... Forget about that matchup, totally fine if you lose it. "Can't win them all!".

missing Keli'dan the Breaker . What instead ?

Hysteria, I actually want it twice in the deck because the card is kind of too nutty and good even after nerf, but just can't decide what cards to take out. Maybe cthuun and valdris for 2 hysteria. Dont got kelidan i think hysteria would be best... although some cases I guess board clears like felbreathers and maybe deathwing do a better job and are more kelidan-like cards. But something tells me that you cant really go wrong with an hysteria, that card can do unspeakable things for 3 mana it is absurd...

Valdris is insanely relevant and useful for my matches at least, I've played it a couple of times now and every time it has been game deciding. For one it is because it draws 4 cards so if I am out of gas and used all clears (we all know how insane boards some decks like arbor druid can build in early games these days), it refills my gas and I have the rest of my essential board clearers. Secondly it is a small bonus to dark skies, bigger hand means stronger dark skies, but that effect is minor so I'll concede that that part of valdris synergy is minor, however synergy nonetheless! Third and last but not least, it synergizes enormously with Y'Shaarj. You corrupt a lot of cards with this deck during a match and at the same time you are handlock/control lock, so more often than not you can use valdris to increase your hand size, which is relevant because as a handlock you often keep a lot of cards in your hand for the best moments and you play very greedy, and Y'Shaarj with Valdris basically just makes your Y'Shaarj more playable and viable and effectively just gives you more corrupted 0 cost cards. This last effect and just more card draw for more board clears vs aggro both have won me multiple games and have been very game deciding.

Also I should change elysiana for harrison jones in the decklist because elysiana is never important (literally only vs bomb warrior to "cleanse" your deck of bombs which is very niche to tech for in my opinion), and without harrisson or other forms of weapon destruction you stand zero chance versus weapon rogue. I mainly use it to counter either doomhammers by shamans or self sharpening blades from rogues, you use tapping valrdis, twisting knowledge and sphere of sapience to try get it out of your deck and into your hand asap i guess... 

Something tells me this deck might get more attention than it deserves, but I just really like that twisting knowledge, i think it is my new favorite card, i get extra hellfires shadowflames twisting nethers and dark skies versus those annoying aggro decks and theres a lot of them, and i dont get punished for putting them in my deck versus control decks, because that case i just choose to discover some big threats instead and it still works. 

Cool, in denial
We're the cruel regulators smoking
Cigaro, cigaro, cigar

ahahah dude me too from 1988 Double Dragon muthfvcka

if was 1 or 2 years ago several wannabes would be posting here "GREAT DECK 100% Victory" "SMART" Whatever...and many would be tricked into build this (see Kibler, dekks and other ultimate deck doctors that ain't play shit)
Guess now ppl are more smart in this game, they now know they will get shafted if they choose to copy "pros lists" that's why we don't see many lists like this one. And sincerity above everything, not lying and telling us that this is 'THE DECK".

Fun list, thanks for this.

Keleseth card was the best

Hope they bring it back

HOW is it possible at all?

Elysiana, Cthun and Valdridge are not that useful. You win the late game battle anyway because you mill 10 of their cards, which is a third of their entire deck.

I have noticed elysiana being useless a lot of matches i recommend switching her for harrisson jones or other weapon removal, cthun gives you lossa 5 drops which the deck heavily lacks i recommend keeping it in (plus the gimmick of the deck is big deck so cthun is obvious), valdris i havent played enough to have a good opinion on. I agree with you on elysiana but valdris i dont know.

Gotta say, this is one of the more fun decks I’ve played in a while. Been using it to climb this month and it’s netted very positive results!

Twisted Knowledge is amazing. It almost always has an answer to whatever I’m facing - vs aggro rogue it gave me Fire Breather and dark skies. Rez priest? More twisting nethers! I even got to win a game as Jaraxxus which was awesome :) 

Thank you for this deck. I may have gotten lucky with win rates today as I’ve only lost against Libram pally, but even that loss was a ton of fun!

QUICK UPDATE: 

Versus paladin keep twisting nether in your beginning hand! Also try get board clears out of twisting knowledge! play TK early and keep it in your opening hand! Getting Shadowflame out of it happened to me like twice in a row and with 0 mana 6/6 strongman or using it to clear AND sacc your own rustwix is game deciding!