Iron Mage MK II Specs! · 9:17pm Mar 7th, 2020
The latest chapter of the Under Her Iron Skin storyline has gone live! Now that the first story is almost done (There should be one more chapter and an epilogue) I've got a good handle on what I want Twilight to be capable of, I thought I'd write another post about Magic and how it applies to the Iron Mage armor. Some of this I posted last time, so it might be familiar. If you think my view on magic is interesting, click on the tag #How magic works and see my other posts. I'll try and write my blogs on the subject if it's popular enough.
The version of the Iron Mage suit used in this story is only the second iteration of the Iron Mage armor. It looks very similar to the Hypervelocity version of the suit.
Twilight hasn't built very many suits of armor before so it's not very flexible. Her next suit will take more inspiration from Models 2-4 from the main comics continuity, which was designed by Steve Ditko. 
Unicorn Magic/Enchantments
Unicorn magic is, in essence, wishing. Anyone with sufficient power can do anything they want. But unfortunately, the laws of nature don’t like to be broken. The more widespread or unfocused the wish, the more power it takes to cast. That’s what spells are; you are spelling out, as clearly and concisely as possible, what you want. It's also important to take into account the effects of each spell as you layer it on an object like the armor; if you aren't careful, the effects of the spell could conflict with each other. In order to give herself super-strength, Twilight had to be careful that the spell she used wouldn't affect the spells she used to make the metal lighter or more flexible. Theoretically, you could apply as many spells as you wished over something as long as you found a way to align them, but in practice, you won't be able to apply more than a dozen.
This version of the Iron Mage has enchantments for increased strength, mobility (relative to other people wearing equitably heavy armor) glamour that changes both her voice and magical signature, and anti-corrosion spells that protect it from decay. In addition, Iron Mage has a complex mesh of defense spells that can be re-worked on the fly to compensate for different kinds of attacks both mundane and magical. The current suit has no spells in place to protect Twilight's mind from invasion, trusting her own willpower and intelligence to overcome such attacks. Later suits will need to rectify this.
Twilight knows hundreds of spells, but only a few functions in a combat environment. Teleportation is the least useful of these, as it requires longer to cast than most and a period of time before it can be cast again. It's mostly useful as a means to store the Iron Mage armor in the space Unicorns pass through when teleporting, called the Between by researcher Estee. Her telekinetic power, while strong enough to bend steel, also isn't fast enough to be of use against a prepared opponent.
Her combat spells include a variation of the gravity spell she uses to climb Sombra's tower (timestamp 3:47), a force field, a magic beam that functions like the old-school pulse bolts, the ability to make a half-way functional copy of most spells she sees, the ability to create illusions, and some kind of Fail-Safe spell that undoes magical effects (though she has to put enough power into it to overcome each instance of the spell itself.)
Pegasus Magic and the Repulsor Flight System
Pegasus magic automatically lessens gravity and inertia by a certain amount and gives its user a special awareness of the weather around them— a 'Sky Sight' if you will. It lets them see heat and cold overtop of their normal vision and tracks the motion of the wind around them, though Twilight can't use the latter feature through her armor. Pegasi can also influence the weather within a range of their bodies. Most Pegasi use this to improve their flight, but with extensive training, they can permanently impact the weather conditions within that range. While the range of influence each Pegasus holds is different, none can exceed more than half a mile. Pegasus magic is far more long-lasting than Unicorn magic for unknown reasons that continually frustrate Unicorn researchers almost as much as choice remarks from Pegasus researchers do.
The Repulsor Flight System that Twilight uses is one of a kind. Its design is rooted in a hoofheld weapon she invented called the Spark Hoof-cannon. It interfaces with its user's magic field and then projects raw mana as a short-range energy blast. It's built into a boot and that same energy can be used to leap incredible distances. It's too expensive to market to civilians as of yet, but they were one of the things AIM stole before Twilight ousted them from her company. The system Twilight is tuned to work with Pegasus magic specifically, and cannot function with Earth Pony or Unicorn magic engaged. Enchantments laid overtop each jet provide the energy beam with more focus, allowing a shorter-range thrust to fire indefinitely without damage to the jet and more accurate long-range strikes.
The wings themselves are quite unremarkable, being simple prosthetics outfits with repulsors and made to see sustained combat. Aside from the Repulsor cannons, such wings are common throughout Equestria.
Earth Pony Magic
Earth Pony magic is incredibly variable, depending entirely on what Cutie Mark its user has. Pinkie Pie's allows her to do anything so long as it's connected to making someone happy, Applejack can grow plants, Big Mac is incredibly strong, and Cheerilee can teach a class with the CMC in it without any lives lost. Twilight, when using Earth Pony magic, has the ability to see any form of magic being used, not just spells she casts herself. It also lets her process information most more quickly than she otherwise can (which is already impressive) but she doesn't have any weapons that work with or take advantage of it yet. She is considering an exo-skeleton, not unlike the Undersea Armor but designed to survive a greater variety of environments. 
Misc
Twilight currently lacks non-magical weapons in the suit as she greatly underestimated the power drain that the suit can have, she elected to include two miniature crossbows in her forelegs. They lack the power and range that full-sized crossbows have, but her arrowheads are enchanted to fly far enough to make up the difference. The enchantments on them will release a concussive force that she can alter before firing; anywhere between that of a knockout punch and enough to destroy the stone.
Another feature inspired by her attempts to free the Expo are the emergency Gossamer Wings that activate if something disables the normal wings. These are more fragile than the mechanical wingset and not recommended for combat.
Her most useful innovation, and indeed the reason Iron Mage exists at all, is her Arc Reactor. This was entirely Dinodes idea (he's currently running a roleplaying game called Shagri-La: Rise of the Seekers you can check out for yourselves!) and is based on the Thaumatic Thingamajig Sci-Twi used in Equestria Girls. She can use it to steal magic from both people and artifacts, but can't use any of the function of the suit while engaging it. It's a modification to the device that kept Twilight alive when AIM's attack left her unable to generate magic on her own.
Ooh. Thank you for the overview, it was a fun and thought-provoking read!
Fascinating idea ;)
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Thank you both!