There is no question the warlock's hero power is fantastic for the most part, card draw is very powerful in a card game like this. Despite it's heavy costs, card draw makes it worthwhile. I see this as an opportunity to introduce some ideas to not only spice up warlocks but make their demons a greater asset in a deck. Without further ado, lets get going!
Card: Master Demonologist
Type: Minion (4 mana cost, 2 attack/ 4 health)
Effect: While on the field, all effects of summoned demon minions which cause damage to allied minions or the player are negated. Also, effects triggered by demon minions which require an allied player to discard cards are negated as well.
Comments: This card has low stats because its not meant to fight, its meant to act as a way to make your demon(s) overpowered. Why would this be balanced? Those effects are only negated when this is on the field; a silence, a polymorph/hex, or straight removal stops this effect. This minions is more a support minion; but it would allow someone to unlock the true power of their demons without cutting their arms off in the process. Also there are only two per deck so unless you get screwed by RNG in arena its unlikely you'll have to face more than two.
Type: Minion (5 mana cost, 5 attack/8 health)
Effect: This card cannot attack. Once per turn this card, using the attack command, can heal an allied minion or player. Using the attack command lowers the attack of this minion by 1. When this minion's attack reaches 0 it can no longer use it's effect.
Attacking a allied minion will heal it for 3 points of damage, attacking the player will give the player a Healthstone (0 mana effect: restores (3+ Soulwell attack upon receiving this card) health); using this effect on the player will consume 3 charges.
Comments: This would be a powerful healing card for a warlock that could be used to either heal their minions or themselves. To balance it, short of using an attack damage buff, there is no way to raise it's attack value. As a result this card can be 'situationally' powerful but also can give you a life-saving heal later in the game (up to 8 point heal without any buffs).
Type: Secret (3 mana cost, max: 1 per deck)
Effect:Upon taking fatal damage, this card revives you at 15 health but corrupts 2 mana crystals, making them unusable with neutral spells or minions.
Notes: All warlock spells up to this point can be considered neutral, the corrupted mana crystals work somewhat like shaman's overload effect, only this effect is not necessarily a bad thing. However like the overload effects, these corrupted crystals become purified one at a time over time.
Comments: Warlocks finally get a secret! This also fits well with the whole warlock theme, a cool and useful effect at the cost of something. Rather than have it destroy to mana crystals I see this as an opportunity to introduce the concept of corrupted mana crystals. These mana crystals I plan to be used as a fuel for some really powerful spells that normally either have huge costs or cannot be used at all. You might say this is a ripoff of mage's Ice block but ask yourself this, have you ever seen a mage in WoW use iceblock when they're about to die? no, they tend to use it to block lots of burst or atleast the smart ones do. On the other hand a soulstone can be used to finish off an enemy by reviving quickly and hitting them while they're down; effectively they don't know you will revive up on them its a Secret, get it?
Game Concept: Corrupted Mana Crystals
All demon related effects that destroy mana crystals no longer destroy them, instead they convert mana crystals into corrupted mana crystals. This corrupted mana is used as a fuel for certain spell effects and possibly demons. While a crystal is corrupted, it cannot be used as a normal mana crystal. Every turn you lose 1 corrupted mana if you have any. effects which require corrupted mana will also purify your mana crystals.
Comments: if the development team is worried about a long devlopment cycle here, you shouldn't worry. The effect is very similar to a shaman's overload effect only it would hopefully look different. The only big difference here is the corrupted mana can be used as a resource just like normal mana. The other big thing is you'd need cards that would work in concert with this. I've provided some ideas below that will help flesh out the concept.
Type: Spell (4 corrupted mana)
Effect Hit the enemy hero with a blast of shadowflame dealing 4 damage; if your enemy it at 15 or less health, this ability does 8 damage.
Comments: Like its history, this card is finisher designed to finish off your enemy. If corrupted mana becomes easy to obtain the cost of this ability may need to be adjusted but as of right now this can be used as a great way to finish off your enemy.
Card: Demon Soul
Type: Spell (0 mana cost, max: 1 per deck)
Effect: Consumes 3 unused mana crystals and converts them into corrupted mana crystals.
Comments: the reason this has a 0 mana cost is it would be terrible if it has any because assuming you don't have the cards to use the corrupted mana this would cost 4 or more mana which might be used to summon a minion or perhaps remove some minions. This card is limited to one per deck to prevent it from becoming insane.
Card: Chaos Bolt
Type: Spell (4 corrupted mana)
Effect: Launch a bolt of chaotic energy dealing 4 damage plus 1 for each allied demon to a target. This ability ignores armor effects.
Comments: Boom! Chaos Bolt! and like the way it used to be it goes right through absorption and armor effects. its a powerful spell that gets stronger the more demons you have. Its cost is high since of how scarce corrupted mana is at the moment.
Card: Verdant Spheres
Type: Weapon (6 mana cost 2 attack/6 durability)
Effect: Upon using this weapon to attack it costs two durability. when a allied demon deals damage to an enemy minion or hero converts 1 mana crystal to corrupted mana and lowers the durability of this weapon by 1.
Comments: another way to generate corrupted mana that also doubles as a weapon, but like the spheres themselves, using them for an attack will only net you three hits. The high cost of the ability fits in well with the warlock theme.
Card: Demonic Rebirth
Type: Secret (3 mana cost, 4 corrupted mana to activate)
Effect: When an allied demon is destroyed and you have enough corrupted mana, this card activates, reviving your demon at full health but does not activate any special effects.
Comments: Imagine how awesome this would be, you use power overwhelming on a dread infernal, bringing it to 10/10 then use void terror, the secret triggers and it respawns back at 6/6 along with your now empowered 13/13 void terror.
Card: Archimonde, The Defiler
Type: Legendary Minion? [lol] (5 mana cost, 5 corrupted mana, 10 health cost, 6 attack/10 health)
Effect: Archimonde's arrival applies an AoE silence effect to all enemy minions. Archimonde cannot be targeted by hero, spell, or minion effects.
Comments: heh, a minion... But seriously holy hell hes so powerful but remember you need 10 total mana, you need to perfectly balance your mana between corrupt and pure and it still costs you 10 health to use him. Also because its 10 total mana, you cannot summon other minions this turn. So yes, super scary and super powerful but a royal pain to summon.
Type: Minion (6 corrupted mana, 5 attack/4 health)
Effect: This minion whispers tainted promises of power into the ear of a random enemy minion causing you take gain control of that minion for 1 turn.
Comments: Intelligent and cunning and still a formidable combatant. But no pure warlock can summon this fiend only one corrupted with atleast 6 mana can hope to bring forth this minion. the high corruption cost is the cost for bringing this minion out.
This has been my warlock ideas to improve them. I'd like to touch on some points I wish to make before I'm done here. 1st, The reason corrupted mana is a good idea is its something warlocks have to manage but it can also be an asset to a warlock if used properly. A skilled warlock will balance this resource in such a way with its normal mana to allow the warlock to wreak terrible destruction. This resource will add a skill ceiling to warlocks that revolves around how well someone utilizes the effects. 2nd I honestly wish to add more ideas to spruce up demon synergy, but I'm fresh out of ideas. I think there needs to be a card or cards that make your demons more useful and not so self-destructive to the warlock. 3rd I know Archimonde looks overpowered but honestly he is the minion (lol) for a player who wants to wreck face. His biggest weakness is he can be cut down by minions while still being very expensive, also he is not immune to AoE effects.
Any comments are welcome especially from the Hearthstone Team if you guys have a spare few minutes; If not its ok. I ask if you do comment that you keep it PG-13. Thank You!