My idea would be as follows...

It would look something like this. Maybe not as dark, I'd say it has the black armour-type bits, but instead of fire coming out it glows a dark purple. It has the two arms, and tapers off at the bottom.
Demigod Name: Bane (working title... I'd like to see something better.)
Basic Description: Bane is a personification of the fear that the Gods inspire in those in the world. All of their nightmares, fears, and phobias are all channeled into the one place even the Gods themselves fear. Bane is the Keeper of Fear, the Dread Lord of Terror. His very form is fear and terror, and channels his essence into his enemies who are quickly routed and slaughtered.
Bane is an assassin Demigod, able to disrupt and destroy enemy Demigods' ability to fight. He is very mana-dependant, but his spells and abilities are strong. His health and autoattack damage are below-average to offset this. He would have the following abilities:
Grip of the Dark One: (Channeling) Stuns a target Demigod (similar to ub's grip). The time a Demigod is Gripped is based on level, but is dealt no damage. Instead, when it is freed, the victim's armour is reduced by 30% for a short duration.
Channeled Terror (Level 15 special): The target is also slowed by 15% when released.
Umbral Rip: Targets an area, all enemies in the area are forced to move outside of the target zone, and take a scaling penalty to their damage.
The Enfeebling Black: Single target ability, the target takes a very large unstackable penalty to damage, a moderate penalty to health regeneration, and their ability to regenerate mana is removed.
Your Delicious Terror (Level 15 Special): The target is silenced for the duration of this ability, and Bane receives their lost mana regeneration.
Shattering Presence (Passive, Aura): Enemies in the aura receive a penalty to their armour, reflecting Bane's terrifying presense on the battlefield.
The Edge of Life (Passive): Whenever an enemy dies while near Bane, there is a chance that they will heal him for a small percentage of their hit points.
The Dark Lord (Passive, Level 15 special with above two passives as prerequisites): Bane always heals a small amount of damage when an enemy unit dies near him (less than Edge of Life), and each enemy that dies gives a stacking minor penalty to armour to the remainder of the enemies inside the aura. [Note: Essentially, every enemy that dies would heal maybe a third of the HP it would if it had healed him based on the chance of that happening, and when it does die, it gives an extra penalty to armour on top of the penalty given off by the original aura. On issues of balance, this effect is small at best.]
For We Are Many... (Passive, on Death): When Bane dies, his essence remains to continue to haunt the enemy. Similar to Oak's on death ability, Bane splits up into a few flying aspects of fear that last for a few seconds. At the last level, his armour penalty aura remains centered on where he died.