Level 1: Choose a demon to control. While no demon is active, your Health Funnel transforms into one of the following:
Summon Felguard
Summon Succubus
Summon Voidwalker
You can control your demon directly, and they behave like Misha - order them to attack or stand in a specific point, or self-cast to make them follow your hero. The Command Demon ability is on the (1) key by default.
Every demon feeds 25% of a hero's xp to the enemy team upon death.
Level 4
Mana Feed - Passive: you gain 1% of your maximum mana and your demon heals for 1% of their maximum health when your demon attacks an enemy hero.
Demonic Pact - Quest: Gathering regeneration globes increases your active demon's maximum health by 1%, up to 25%. When completed, you gain 25% more maximum mana.
E:
Improved Health Funnel - you regenerate 2% of your mana each second while casting Health Funnel and it heals your demon 10% more.
Level 7
Q:
Shadow Embrace - Shadow Bolt leaves a Mark of Shadow on an enemy hero for 5 seconds, increasing your active demon's damage to that hero by 50%.
Q + W:
Shadow and Flame - Shadow Bolt reduces Hellfire's cooldown by 4 seconds, and Hellfire reduces Shadow Bolt's cooldown by 0.5 seconds every time it hits an enemy hero.
This includes the damage over time, which ticks every 1 second for 5 seconds.
W:
Inferno - Hellfire can now be channeled while moving.
Level 10
R1:
Demonic Empowerment - improves your starting demon. Only one of the three effects can be chosen, depending on what demon you chose at level 1. The other two are locked, and can never be picked.
1. Summon Felguard:
Decimation - Felstorm now has a 10 second cooldown.
2. Summon Succubus:
Pleasure Through Pain - While your Succubus is active, your Shadow Bolt deals 100% more damage and its cooldown is lowered by 1 second.
3. Summon Voidwalker:
Torment - the duration of Suffering is increased by 0.5 seconds, and the damage taken by the Voidwalker instead of your hero through Soul Link is increased to 40%.
R2:
Master Summoner - you may now summon any of the three starting demons. You gain access to a new ability, Cycle Demons, hotkey (2) by default, which cycles through the three demons, changing which one will be summoned next (and the icon of the ability reflects this). If a new demon is summoned while you still have an active demon, the new one replaces the old one and the summoning ability goes on a 10 second cooldown.
Note: You may never summon the same demon you are currently controlling until it dies. You may, however, summon a new, different demon while you are controlling another starting demon; to do this, self-cast Healing Funnel. It will begin channeling the summoning spell, but also make your active demon unable to attack or use abilities, as they are preparing to go back into the void. The point of this is: it's not very beneficial to summon a new demon in combat if your current demon is still alive. If you're in Metamorphosis, it might suddenly turn out to be more useful, as the summoning is instant.
Level 13
Soul Fire - Passive: Your active demon's basic attacks improve the damage of your hero's next basic attack by 50%, up to 500%.
This is the only time it's worth auto-attacking with this hero.
Demonic Sacrifice - Passive: When your active demon is killed
(not unsummoned, killed), you instantly gain 25% of your maximum health, and your next demon summoning is instant regardless of Metamorphosis. This effect has a 20 second cooldown.
D:
Fel Synergy - Every time one of your abilities hit an enemy hero, the cooldown of Metamorphosis is reduced by 1 second, but Metamorphosis now only lasts for 12 seconds.
Level 16
Q:
Shadowburn - Shadow Bolt's damage is increased by 200% on targets affected by Hellfire's damage over time effect.
Q:
Shadowfury - While in Metamorphosis, Shadow Bolt now hits all enemy heroes in range.
W:
Cremation - Each tick of Hellfire on the same enemy deals 10% more damage to them, stacking indefinitely.
W:
Backdraft - Increase Hellfire's damage by 300% to all targets including YOURSELF.
Level 20
R1:
Demon Soul - improves your starting demon. Only one of the three effects can be chosen, depending on what demon you chose at level 1. The other two are locked, and can never be picked.
1. Summon Felguard:
Impending Doom - The Felguard deals 100% increased damage and gains 25 armor when below 50% health.
2. Summon Succubus:
Irresistible - Seduction's cooldown is reset to 0 if the previously seduced target has not taken damage for 5 seconds. In addition, each of Succubus' ranged attacks now applies a stacking 25% slow instead, up to 75%.
3. Summon Voidwalker:
Nether Ward - While your Voidwalker is active, both you and him gain the Nether Ward passive, which grants 40 spell armor at all times.
40 spell armor + 40% Soul Link. You better start right clicking, pumpkin
R2:
Legion - you may now control all three starting demons at the same time. To cast their heroic abilities, cycle through them with your Cycle Demons ability (2) - this will cycle their heroic abilities on the ability bar. Outside of heroic abilities, you can either control the demons individually with the Command Demon (1) ability when one of them is selected, or as a group with a new Command Legion (3) ability, which simply makes all of them focus the same target or stand in the same area.
If all three demons are alive, you cannot summon any of them in combat until they die - this simply followes the rules of summoning stated earlier.
Summon Infernal - a new activable ability. Instant cast: After a 1 second delay, summon an Infernal from the sky, dealing high damage in a large target area and stunning all enemies for 1.5 seconds upon impact. The Infernal replaces your currently active demon for 20 seconds, dealing high area of effect damage with each melee attack, and passively deals moderate damage to all enemies near it. The Infernal cannot be replaced by a new demon until it dies or leaves the battlefield. Cooldown:
180s
Summon Doomguard - a new activable ability. Instant cast: After a 1 second delay, summon a Doomguard at the target point. When the Doomgard arrives, you immediately enter Metamorphosis, or if already in Metamorphosis, you extend its duration by 10 seconds. The Doomguard has 50 armor, and it replaces your currently active demon for 20 seconds, dealing very high single-target damage. The Doomguard cannot be replaced by a new demon until it dies or leaves the battlefield. Cooldown:
180s
Heroes of the Storm Build Guides
Good concept though, anyway! Hellfire could use a bit of a rework to be less self-destruct-y, like having it channeled on an enemy to deal area damage around them. Casters like Warlocks aren't really the type to be in the middle of a fray to begin with, but hey, it's your concept and I don't actually play Warcraft, so do what ya like!