This will be of interest only to those of you who are big on general theories of Bungie games:
The most popular general theory-related hypothesis about the Great Devoid is that there's a sleeping W'rkncacnter at the bottom of it, perhaps the same one which, in our timeline, sleeps below a pyramid in Central America. Now, regardless of where they were intended to appear originally, in the finished Myth series the Mahir only appear in the second game; that is, after Balor's head has been thrown in the Great Devoid and detonated. Doesn't that suggest that the Mahir are actually the dreams of a god disturbed in its sleep? If the Mahir had existed before, surely Balor would have recruited them and used them in ambushes and as bodyguards, as Soulblighter does.
I'm struck by the similarities between the Mahir and PID's Phantasms. Both are incorporeal beings, more alien than any other in their respective games, capable of absorbing energy directly from their foes, immune to many types of damage and completely black (presumably because of their ability to absorb light energy). I think (assuming there is a Myth-PID link) that the Mahir are the Phantasms of the Myth world. There may be a whole PID-like network of caverns at the bottom of the Great Devoid (tunneling Dwarves, beware), with the Mahir the only dreamed creatures capable of climbing out of the hole.
Regarding the shadows of Shades theory: This is hardly a conclusive disproof, but traditionally living shadows and other creatures made from darkness have been especially vulnerable to radiant energy (light and heat) attacks; adding energy to them dilutes the darkness of which they are made. Yet the Mahir are most certainly not; as a matter of fact, they're immune to both fire and lightning. This indicates to me that the Mahir are not creatures actually made out of darkness; rather, like the Phantasms, they are creatures who require energy to sustain them in the ordinary way and use a shell of darkness to absorb it. Pumping radiant energy into a Mahir only strengthens it. I hope drawing a distinction between the two types of creatures
(those that are darkness and those that use darkness) makes as much sense to you as it does to me.
While I'm on this, what of the referring to magical attacks as "dreams?" Perhaps this is literally true; perhaps the influence of the W'rkncacnter gave the inhabitants of the Myth world the ability to do (on a much smaller scale) what the W'rkncacnter itself can do; alter reality through one's dreams and imagination. If this skill is at the foundation of all Myth magic, it's no wonder that sorcery requires a powerful intellect and years of practice; it's a rigorous mental discipline, learning to send yourself into a waking-dream-state and then imagine the changes you want to make in reality as vividly as possible. (This doesn't conflict with Shiver being an idiot; maybe she spends all of her mental energy on magic and none of it on figuring out how to do things like tie her shoes.) The dreams may require power sources (the energon cubes) because, unlike the W'rkncacnter, humans can't actually violate any laws of nature (like conservation of energy) with their dreams. All they can do is move around existing mass and energy.
--SiliconDream