I think we can all agree that the current demo lock is not exactly good.
I'd like to see demo as a hybrid spec. Both range and melee. If you have played FFXIV Red Mage, you will understand what I mean, though it wouldn't work the same.
The spec would swap between range and melee depending on how much of a resource you have. Once you reach max, your abilites change into melee attacks. This is where the majority of damage comes in. Sounds a bit similar to how meta was like with lock, pop meta, spend your resources on powerful attacks. So how would this version work? Well ive come up with some ideas of spells and mechanics.
Resource
Fel Energy 0-200
Your range attacks generate Fel Energy and once you reach max energy, you have access to the ability Nefarious Incarnate, where you hulk out into a form similar to how Gul'dan looked when he transitioned to phase 2 and lunge towards your target.
While hulked out, your Fel Energy drains at a rate of 10 p/s and theres nothing you can do to prolong it, but you now have access to brand new spells.
Abilities
Shadowbolt - Generates 15 Fel Energy 1.5 sec cast 40 yrds - Fire a ball of shadowy energy, dealing x amount of damage to the target and each target afflicted with Fel Infused. Has a 50% chance to activate Demonbolt
Demonbolt - Generates 25 Fel Energy Instant Cast 40 yrds - Conjure a shard of demonic energy and launch it towards your target, dealing x amount of damage and applies a dot effect equal to the damage dealt over 5 seconds.
Eye of Gul'dan - 20 second cd Instant Cast 40 yrds - Summon an Eye of Gul'dan to gaze upon your target, dealing x amount of damage over 5 seconds to enemies within 10 yrds of the target and applying Fel Infused to each target hit.
Fel Infused - Debuff from Eye of Gul'dan - 5% increased damage taken for 5 seconds. Refreshes duration from each hit.
Hand of Gul'dan - Generates 30 Fel Energy 20 second cd - Summon a demonic meteor with a random demon inside. Dealing x amount of damage to the target and releasing the demon from within. A random pick from 3 demons can be summoned. Lasts 10 seconds
Imp - Casts a fireball at the target, dealing x damage and granting the Warlock 5 Fel Energy
Felhound - Bites the target, dealing x damage and increasing the chance of Demonbolt activating by 5%
Observer - Gaze towards the target, dealing x damage every second for 10 seconds, increasing by 10% every second.
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Once you reach max Fel Energy and use Nefarious Incarnate, your spells are changed/upgrades
Shadowbolt = Sever
Demonbolt = Expunge
Eye of Gul'dan = Fel Scythe
Hand of Gul'dan = Empowered Hand of Gul'dan
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Sever - Melee range no cd - Sever your target, dealing x damage. Critical strikes activates Expunge
Expunge - Melee range requires proc - Attempt to destroy the targets soul, dealing x damage and applying Damaged Soul to the target
Damaged Soul - Debuff - Damage taken increased by 5%, lasts 10 seconds, can stack.
Fel Scythe - 10 yrds costs 20 Fel Energy - Slice in front of you, dealing x damage to all targets within 10 yrds. Each successive Fel Scythe increases the damage and cost of Fel Scythe by 20%
Empowered Hand of Gul'dan - 1 charge - Summon a huge demonic meteor with a powerful demon inside, dealing x damage to the target and releasing the demon from within. A random pick from 3 demons can be summoned. Lasts 10 seconds. You gain a charge each time you enter Nefarious Incarnate
Fel lord - Bladestorm - The Fel Lord becomes an uncontrollable storm of destructive force, striking all targets within 8 yrds. The Fel Lord follows its target
Pit Lord - Blitz of Destruction - The Pit Lord unleashes a powerful attack on the target, dealing x damage
Inquisitor - Demonic Transmission - Channels into the target and transfers a portion of the targets powers into the Warlock, decreasing the targets damage dealt by 5% and increasing the warlocks damage dealt by 5%
Once your energy is reduced to 0, you are launched back 30 yrds and stunned for 2 seconds.
This is just something I mashed together for a bit of fun, but what do you think?