Hearthpwn

I tried different builds based on Stealer of Souls, starting with more Zoo-oriented approach, than trying Big Demon and finally settling somewhere between with most of the soul shards package included. With this version I managed to reach legend, getting 7 wins in last 8 games played on D2-D1. Explaining card choices below:

Demonic Studies - cost reduction (Stealer of Souls played turn 3 is much better than played turn 4), value, (especially with Tamsin Roame) and you really want to get Tickatus against Priest (preferably doubled with Felosophy);

Felosophy - you might keep it if you have it in your starting hand on the left to double and buff early demons especially in faster matchups, buffing and doubling Stealer of Souls might also be worth it, as even if they get rid of the first, the second one has much higher chance to survive. All in all this card is very versatile, doubling Man'ari Mosher to get huge life swing or big demons to win with value, or any useful demon (cough Tickatus) you got from Demonic Studies. Always check if the demon you want to double is really the cheapest one!;

Spirit Jailer - part of soul shards package, early drop and demon;

Darkglare - one of the first cards that made the cut when I played Zoo-oriented version and one of the last added to the current one. But it is mana cheat, its synergy with Stealer of Souls is insane and I needed to increase number of demons in the deck to make Free Admission discount more consistent, so it fit quite well. It can be also quite good early drop to pull removal before casting Stealer of Souls; seems it just too situational and too weak for this deck, so instead:

Fire Breather - surprisingly useful, especially against aggro meta (though you need to remember about demon tag, especially against Demon Hunter and Hunter), hurts almost none of your minions (Kanrethad Ebonlocke is especially sad exception). Especially great against Token Druid.

Kanrethad Ebonlocke - demon lord, early drop, mana cheat, great board refill and Kanrethad Prime is a nice Felosophy target in late game;

Drain Soul - cheap removal, life gain, great with Tamsin Roame;

Soul Shear - also cheap removal, great with Tamsin Roame and part of soul shards package;

Free Admission - mana cheat and draw. If you can play Stealer of Souls into Free Admission early, it's very difficult for you to lose game;

Man'ari Mosher - quiet hero of this deck. He saves your life and let you make better trades (or just finish opponent), but sometimes you need to tempo play him on turn 3 to prepare ground for Stealer of Souls. One of the best targets for Felosophy especially in faster matchups;

School Spirits - nice mass removal and part of soul shards package;

Tamsin Roame - one of the 3 non-demons in this deck, but well worth it. Doubling your spells is very important, especially as most of them heal you (directly or through soul shards). And she fits mana cheat theme of the deck;

Stealer of Souls - this card is very good. Unless it's totally insane. You can play Lord Jaraxus turn 4-5 with it! Or Enhanced Dreadlord, Soulciologist Malicia, Ring Matron, Kanrethad Prime. Or few of them.

MVP of this deck. If you play it early and it sticks for at least one turn, you are on a very good path to winning this game. Great with Free Admission - lets you play more cards for health and with reduced damage to your face. Remember about visual bug with Felosophy - cards doubled with Felosophy always have their cost shown as mana symbol, but if you copied card you pay for with health, you pay for copy also with health anyway.

Void Drinker - so we play Demonlock with soul shards package. Can't see this card not played. Well, it seems we need to improve control match-ups a bit and we really want to draw soul shards to heal us, so this vanilla taunt got axed. Instead I put in:

Envoy Rustwix - his deathrattle may not have imminent effect like with other big demons, but is without doubts the strongest one. And two of nine primes are demons too.

Tickatus - sadly, Priest is a real deal and you need Tickatus to win this match-up. Preferably doubled or tripled with Felosophy

Ring Matron - big demon with taunt and really useful deathrattle that can be played turn 4 after you hit him with Free Admission. Yes please. In reality though, you probably have you turn 4 already busy playing 2 mana Stealer of Souls, drawing and... also playing Ring Matron for 6 health to protect him.

Soulciologist Malicia - third and last non-demon in this deck. But soul package without her would be just stupid. Board swings she provides can just win game by themselves.

Enhanced Dreadlord - worse Ring Matron. 2 mana is a big difference, still it is big, has taunt and leaves good minion behind, so it makes a cut.

Lord Jaraxxus - if you pay for him with blood you lose only 4 health. Turn 4 stealer into turn 5 jaraxus being immediately able to use his hero power? This is pure madness.

 

Cards that did not make the cut:

Flame Imp - tried it with more zoo-oriented approach, but additional health loss hurts too much. Especially with Felosophy or...

Raise Dead - this card is not bad, but others just fit better. And it is random, has anti-synergy with Soulciologist Malicia or Ring Matron, doesn't work also that well in non-Zoo Warlock

Archwitch Willow - I really like her. But she is too slow. Anti-synergy with Free Admission and low cost demons decrease her value.

Enslaved Fel Lord - big demon with taunt - but no deathrattle, so very easy to remove and make you pay a lot for it. And even left on battlefield he makes little pressure.

Tickatus - yes, big demon with great effect against Priest. You might consider him if you play against Priest meta, but we have Shaman meta and he is just too weak against faster decks. well, Priest seems to be to big part of this meta not to include Big Tick.

Fire Breather - 2 damage to non-demons is nice, but just not enough for 4 mana, 3 health is also not impressive. You might consider her if token druids haunt your dreams.

Backfire - yes, it draws one more card than Free Admission, but additional health loss is hard to swallow and no cost reduction makes it even worse with Stealer of Souls

Luckysoul Hoarder - he seems like an obvious addition as part of soul shards package, but not being demon is why he did not make a cut. I would be happy to include him otherwise (also nice draw to play him after Stealer of Souls.

Tour Guide - yes, it's awesome to play Stealer of Souls into hero power for 0, but it's very narrow effect and the card itself is just to weak. Not a demon too.

Mortal Coil / Final Gasp - some potential with faster match-ups, but overall too weak.

So if you're tired with Controllock as only choice (and quite a bad one in this meta), you might want to try it. Nobody plays Stealer of Souls in standard so you will catch a lot of people by surprise.

edit history: -2 Darkglare, -2 Void Drinker, +2 Fire Breather, +1 Tickatus, +1 Envoy Rustwix