Hearthstone: Knights of the Frozen Throne - Bloodreaver Gul'dan Demonlock Deck
Demonlock deck has evolved and changed from time to time but this time with Bloodreaver Gul'dan, it's a truly Demonlock deck. I believe Demonlock deck is the tier 1 deck among all Warlock decks in KotFT.
Defile is a card that can turn the tide when it comes to AoE in this deck. Defile + Tainted Zealot combo can deal 5 damages to all minions — it's a lot effective than Hellfire.
In addition to the combo mentioned above, Tainted Zealot can be combined by other spells. It's not exaggerated that this is a "legendary" card in this Demonlock deck.
You may prefer Drain Life than Drain Soul. The fact is Drain Soul comes with Lifesteal which can be enhanced by spell damage boost, means if you deal 4 damages with Drain Soul you gain 4 HP for your hero, that's not so bad compared with Drain Life.
Happy Ghoul is not for Priest only. Use this card and another healing spell / minion to build a combo.
The stats and special effect makes Despicable Dreadlord a "legendary" demon card.
Not only its hero ability but also the battlecry are amaaaaazing.