Kil'jaeden by Darkomicron

Kil'jaeden is designed as a damage dealing specialist hero who focuses on buffing and debuffing as well as using the terrain. I thought this would fit in very well with his fantasy as a strategist and his reputation of being merciless to his subordinates. He should be a strong laning hero who later works together with his team by empowering them or weakening the enemy.

I had a hard time picturing him on a horse, so I gave him a different kind of mount.
It's just a normal mount, but hero specific like Diablo's Terror Charge.

Level 1:
Empowering Mark: Increases the damage done by the target of Mark of Sargeras to 25%.
Assimilate: Gain one charge of Assimilate per hero takedown, with a maximum of up to three charges. Assimilate instantly kills target neutral Mercenary. (Bribe)
Destructionist (Demolitionist Kil'jaeden specific): Basic attacks against structures deals 25% additional damage and destroy 1 ammo per hit. (Demolitionist)
Reaching Flames: Increases the range of Felfire by 30%.

Level 4:
Siphoning Orb: Allies gain 20% lifesteal while Orb of Kil'Jaeden is active.
Destruction Orb: Enemies take X (+x per level) damage while Orb of Kil'jaeden is active.
Rise within the Ranks: Activate to cause an allied lane minion to take 50% reduced damage, and deal 100% bonus damage. Lasts 30 seconds. (Promote)
Fel Power: Increases damage done by Kil'jaeden's basic attack by 15% and grants 15% lifesteal.
Splitting Flames: Kil'jaeden's basic attacks now hit two additional targets for 35% damage.

Level 7:
Flourishing Flames: Fel Fire now explodes in a cone after hitting it's initial target. Dealing X (+x per level) damage as well as leaving Fel Flames in that area that burn for 2 seconds dealing damage.
Flaming Nether: Upon using Netherwalk, Kil'jaeden will leave Fel Flames that last 2 seconds and burn enemies. Lasts 6 seconds.
Might of the Legion: Upon activation, Kil'jaeden's cooldowns regenerate 30% faster. Lasts 10 seconds. 60 second cooldown.
Shifting Void: Increases the duration of Netherwalk by 1.5 seconds.

Level 10:
Summon Doomlord Kazzak: Kil'jaeden summons his lieutenant Doomlord Kazzak. A powerful doomguard which can periodically cast a Rain of Fire dealing X (+x per level) damage in a medium radius (10 seconds cooldown, can be cast by using the heroic again). Kazzak also attacks nearby enemies with his weapon. Lasts 30 seconds
Nether Anomaly: Kil'jaeden conjures up a ball of energies straight from the Twisting Nether and launches it towards a location. The orb deals X (+x damage per level) per second to enemies in it's path and slowly sucks them towards the orb. The orb can be sent towards a different position every 2 seconds. Lasts 6 seconds.

Level 13:
Wrath of Sargeras: Reduces the cooldown of Mark of Sargeras by 5 seconds and a second charge is available.
Orb of Annihilation: Orb of Kil'jaeden now increases the ally's movementspeed by 30%.
Orb of Corruption: Increases the slow of Orb of Kil'jaeden to 50% when cast on an enemy.
Nether Protection: Decreases damage taken during Netherwalk by 30%.

Level 16:
Shadow Shield: Each ally or enemy you pass through during Netherwalk grants a shield equal to 15% of your maximum health, to a maximum of 60%.
Burn Mortals!: Felfire can now be cast again for free within 4 seconds. The second Felfire deals 50% damage.
Orb of the Legion: Demons are summoned periodically around the target of the Orb of Kil'jaeden. They will attack enemies nearby, prioritizing heroes. If no targets are available they will push the nearby lane. They deal X (+x per level) damage per hit. They last 20 seconds.
Cunning Deceit: Kil'jaeden enters stasis for 3 seconds and gains invulnerability. During this time he can still cast abilities and use basic attacks, but he cannot move. At the end of the 3 seconds deal X (+x damage per level) to nearby enemies in a medium radius. Can be canceled prematurely.

Level 20:
Supreme Lord Kazzak: Supreme Lord Kazzak summons Twisted Reflections and calls them to him. When a Twisted Reflection reaches Kazzak it heals him for 2% of his total health. Kazzak now lasts indefinitely.
Twisting Nether: Enemies are now sucked into the Nether Anomaly faster, and upon reaching the middle are stunned for 1.5 seconds.
Bolt of the Storm: Teleport a short distance.
Fury of the Legion: Every 5 seconds your next basic attack will deal X (+x damage per level) extra to the target, as well as X (+x per level) damage to nearby enemies. (Fury of the Storm)