Mal'Ganis a tanky warrior hero who excels at leeching health from enemies and preventing weakened targets from escaping.
Using his Bane of Agony, Mal'Ganis can inflict DOT on his victim. When they are weak and attempt to flee? Mal'Ganis can quickly close the gap with Darkflight before using Mind Blast to stun them and punish them further. Darkflight + Mind Blast + Vampiric Touch would be an exceptional combination of skills to use to surprise unsuspecting enemies, as well as turning an unfortunate enemy into a prime target for nearby allies.
Mal'Ganis has two heroics that force the other team to react. Nether Vortex moves in a straight line, stunning any enemy it touches and increasing the damage it inflicts the further it travels. When it reaches its maximum distance, Nether Vortex explodes and stuns nearby enemies, forcing the enemy team to be wary of the Nether Vortex as it reaches its maximum distance.
Fel Aura grants Mal'Ganis with more power to harass and push like a true tank, as he receives buffs to amplify his effective while his incoming damage is decreased.
Base Health: 2685 (4.85 point per second regen)
Base Mana: 500 (3 point per second regen)
Basic Attack Damage: 109
Heroes of the Storm Build Guides
I'd say 3.5 seconds is.. Rather long. No matter how easy it may end up being to dodge, that's instantly the second longest stun in the game; Longer than Octograb, easily one of the more frustrating ultimates. Not to mention, no (mentioned) channel time makes it unavoidable at melee range. On a melee hero. Maybe add a channel time and.. Lower that stun. That's something that needs to be done.
Darkflight, untalented, is the fastest mobility option in the game, with a possibility of a stealth. With your wording, that's also stealth that can't be broken by enemies. I'd.. Make that maybe.. 50%? I don't know, bad with numbers, it's just.. Really fast. It'd both make him uncatchable and unescapable.. Especially with almost 1/3 the CD of Cho'Gall's speed and Falstad's Mount, and almost 1/2 of Brushstalker(Dehaka).
Besides those two, I'd say it's a pretty good concept. Well done, and I hope you read this and maybe take it into account.