Hearthpwn

If you're feeling really spicy, you can add in Doomguard and Krul the Unshackled replacing Bloodbloom and Cataclysm.

 

R.I.P Siamat, your awkward power and synergy will be remembered not that fondly but still a nice sink of dust I guess :(

HELLOOOO Valdris Felgorge

Comparisons to old deck. Add in Bloodbloom for consistency, replace Siamat with Valdris, Shadow Bolt replaced by Dark Skies, Doomguard and Krul removed for the Bloodbloom and new addition Abyssal Summoner

 

Update: Replaced Bloodbloom with Prince Taldaram
Edit 2: Removed Twisting Nether, Cataclysm and Prince Taldaram for Doomguard + Krul the Unshackled and Plague of Flames

 

Card writeups:
Renolock. You know how it works and it can generate some serious value. I played around with the idea of Dragons and Handlock packages but it just doesn't fit with the Demon package as well. This version is heavily Demon-flavoured with Mecha'thun as an alternate win condition if you don't have enough value.

Kobold Librarian helps you make a 29 card deck. Just an amazing flexible card

Plague of Flames is here as an alternative to Bloodbloom Cataclysm as a less situational and easier to set up combo piece for Mecha'thun

Corrupting Mist can work with Mecha'thun as well but it's mostly for a solid early game AOE that just works really well

Darkbomb is 3 damage for 2 mana. Good o'l reliable

Defile is defile

Dark Skies is a new addition I believe will fill a good range of roles. Solid turn 3 play.

Hellfire, the standard AOE since Hearthstone's inception

Voidcaller is one of the strongest Demon enablers in the game.

Despicable Dreadlord has a repeatable effect that often heavily dents enemy boards and gameplans. Very solid

Doomguard is here to add to the critical mass of demons. This deck is heavily centric around a demon package and this helps push that agenda.

Skull of the Man'ari. Just an insane card in this deck. Often you can go many turns in a row pulling demon after demon. Creates huge tempo without the mana cost while creating handspace for you to tap. Ridiculous

Abyssal Summoner is a card I can't deny I'm excited for. Works with Brann Bronzebeard and just puts a huge ass Demon with taunt onto the field.

Lord Godfrey is usually Twisting Nether on average with a 4/4 and a mana cheaper, but often so much better that it can bypass deathrattles and reborn and shit like that

Siegebreaker is the most underrated demon in my opinion. Not exactly super mana efficient but it's a huge taunt that has more health than Mal'Ganis while also bolstering a demon board for good offensive pressure.

Valdris Felgorge is THE card of the set. Come on, draw 4 and help power Mecha'thun even more, and just generally hand size manipulation in a control warlock deck? Yes PLEASE

Fel Lord Betrug ok I lied. This is contending for the most underrated demon. Even without Plot Twist, this thing demands an answer if not you keep generating removal and potential value with cards like Emperor Thaurissan.

Krul the Unshackled is the card this demon package is built around. Just dump your entire hand and go all out with this one.

Mal'Ganis, come on now you know why he's here

Voidlord might annoy you with putting 1/3's into your resummon pool, but you can't deny it's power on turn 4-5 when it comes onto the board. Just hard stops so much aggro

Bloodreaver Gul'dan. Play to steadily burn down the opponent. Oh you also get a huge unstoppable board of big ass demons. At least until they hard AOE

Dirty Rat is SO useless in SO many matchups. But then the ones he is good in. Oh boy. You win.

Doomsayer is just good. Turn 2, 3 or anywhere you want to fit him in.

Zephrys the Great is... well come on you play Renolock. same goes for Reno Jackson and Kazakus

Brann Bronzebeard gets you that unfair turns you have wet dreams about. He's insane here.

Zola the Gorgon gets you even more unfair plays. She's insane here.

Zilliax has your back whenever. Healing and taunt and removal on 5 mana? wow ok.

Emperor Thaurissan sets up your combos and just works really well with your control gameplan and huge handsize

Mecha'thun is my favourite tech option in Renolock. Just use him along with Cataclysm or Plague of Flames to blow your infinite value opponents out of the game if they managed to hold on the entire time (I'm looking at you Priest and Mage and infinite armour Druid)