So in other words, the eponymous entities are just NPCs
The idea of TN in the first place doesn't sit right with me, because it gives another way for your huge magic shit to fail and then you're useless for the rest of the fight. Or stuck doing some weirdass random shitty move that doesn't even apply anymore. I understand the purpose of it -Magic is supposed to be high risk, high reward- but I just don't like the flavor or anything else about it, really.
I conccur, it would make sense for another setting and system like Perplexicon where any spell cast successfully is guaranteed to be a threat if you know what you're doing, but here, it just adds another failure clause and makes differentiates magic and physical further. Whilst I agree that magic and physical should have significant differences, those should be on a very limited number of decisive matters, not having what are effectively two entirely different systems, which just makes it more complicated to run and harder to balance.
In fact, I personally (and by this I mean I am not necessarily recommending this be adopted, merely voicing a hypothetical situation) don't see why mana is magic exclusive anyway. Let's take Ashley for example, if she can just shapeshift to an extent, why can't she enhance her physical attacks by contorting her body and bending her limbs at unnatural angles to increase her chances of hitting any enemy trying to dodge? Why can Sen, a master of general purpose magic not pump some of her own magic into enchanted weapons to temporarily empower them? Yes, I am well away that using magic to enhance one's own stats is ICARUS' ability, however she could simply do it with greater efficiency and versatility than everyone else, after all just about all of her systems could theoretically improved by increased power (defensive stats by having electric reactive armor and pumping it into it, offensive stats by pumping into weapons and motors, mobility and accuracy by pumping into motors and propulsion) whilst no one else has the freedom to improve any stat of their choice.
Effectively, it means that MNA actually becomes usable even by characters focused on physical combat. After all characters are so attached to their weapons that they may as well just be similar to spells for them, I mean has anyone ever just picked up a generic gun, shot someone and thrown it away when it ran out of ammo? Does anyone even have a generic weapon? With amount of speculative fiction or magic in half the weapons they may as well be a more limited, modular ability in themselves. Here's a few examples:
Electric Machete - Input mana, increase fine control over enchantment in order to use it as a defibrillator, it ain't going to be pleasant, but it can save lives;
Silver Particle Cannon - Input mana, add radiation poisoning and increases accuracy as high energy particles blasts in atmosphere result in a lot of radiation;
Supression - Input mana, void infusement causing small AOE and increased anti-creation damage;
Phaseblade - Input mana, increase phasing capabilities to ignore even higher classes of armor;
Ceramic Knives - Input mana, increase entropic power;
It may be argued that a MAG roll is required in all those cases, however, from my understanding, stats are used for the actually difficult actions. People don't roll to breathe or require any STR to stand up or carry equipment. Likewise, inputting magic into enchanted or otherwise compatible equipment should not actually require a magic roll seeing as it should be rather easy to do so.
A corollary would be that mana input only work if it should logically be possible. That is, someone with supernatural abilities of one realm would be unable to input mana into equipment powered by another realm unless the equipment has been specifically made or modified to allow it. Effectively, Void can only empower Void without modification. Creation can only empower Creation without modification. Twilight would be the exception in that, the equipment would not only have to be Twilight but also from the same Twilight realm, that is, Jungian Psychiatry cannot power Wall Street and vice versa despite both being Twilight.
Personally, I don't like it, but there are ways to get around the parts of it that make me twitchy. There's still parts of it I don't like
It is indeed far from perfect seeing as it pretty much requires a damn spreadsheet to calculate.