Speculation and Apex Artillery: Mirror, Magic and Mankind · 1:11am Apr 12th, 2015
In the hiatuses (Some part of me insists the plural should be hiati. It is not.) between seasons three and four as well as four and five, two movies featuring an alternate, parallel reality to Equestria inhabited by humanoid creatures were released under the name of Equestria Girls.
The parallel world featured in the movies is accessed from Equestria via a magical mirror dating back up to Star Swirl the Bearded.
This post is me overviewing the apparent relations between the verse inhabited by ponies, which I will call Equestria and the verse inhabited by oddly coloured humanoids which I will call Canterlot High.
The Mirror:
First of all, the two worlds are connected by a magic mirror. There seem to be a few rules that apply to anything passing this portal.
Creatures passing over from Equestria to Canterlot High will assume the form of a humanoid, except if their counterpart (see below) is not one of these. This verifiably applies to ponies and sirens and is presumed to apply to diamand dogs per counterpart theory.
Since creatures returning to Equestria revert to their original form it can be assumed that, similarly, any creature passing from Canterlot High to Equestria will assume the form of their counterpart, or at least that of an Equestrian creature.
Since no cases of the latter have yet been observed, the only thing that can be said for sure about the possible conversion of magic is that the humanoids can not utilize pony magic. However, since pony magic requires wings, a horn or (presumably) hooves to manifest, this does not necessarily mean ponies crossing over to Canterlot High do not retain their magic while in humanoid form. A parallel argument can be applied for dragons.
What is, however, noteworthy is that objects retain their properties upon passing the portal. Both the Equestrian Element of Magic as well as the sirens' gemstones retained their magic, which remained operable.
Magic:
If Canterlot HIgh possesses its own magic, its is not the same as Equestria's, evidenced by the fact the sirens were severely weakened by the lack of Equestrian Magic.
The interaction between Equestrian magic and the humanoids native to Canterlot High produce severe effects.
Sunset Shimmer was, by using the Element of Magic in conjunction with dark magic, able to assume a demonic form with the capability to directly manifest magic.
The magic released by the Element of Magic enabled the counterparts of the bearers of the remaining Elements of Harmony to assume physical aspects (ears, tails, wings) of the bearers as well as function as an assembled team of Elements and bearers and unleash the Power of Harmony. Similarly, Twilight Sparkle assumed aspects of her pony form. Similarly, upon absorbing part of this magic, the sirens were able to assume parts of their Equestrian forms.
Presumably, if enough Equestrian magic were to be released in Canterlot High (e.g. through the complete set of Elements), it would be possible for any native to assume Equestrian features either temporarily when sufficiently aligned with harmony (e.g. in song) or even, and more speculatively, permanently.
Even more interesting is the dark magic used by Sunset Shimmer, which has four possible explanations:
1. The Canterlot High humanoids possess the ability to manifest dark magic.
2. Ponies, and possibly other Equestrians, retain their magic when crossing over to Canterlot High, as well as their ability to manifest dark magic.
3. Ponies, and possibly other Equestrians, retain their magic when crossing over to Canterlot High and can manifest them through use of an Element of Harmony, or possibly another magical item.
4. The dark magic stems from the Element of Magic.
Considering the sirens, the third explanation is not only the least disturbing, but also the most likely in my opinion.
Counterparts:
Many contemporary Equestrians seem to possess a counterpart in Canterlot High that has a presumably identical personality and is either humanoid or an animal. The Equestrian and Canterlot High counterparts also appear physically similar to one another apart from, of course, the difference in their species. An interesting example would be Angel Bunny, whose counterpart is apparently the same as the Equestrian version.
Figures from Equestria's past such as Star Swirl, Clover the Clever or the sirens do not seem to possess counterparts.
While most major and minor characters in Equestria seem to possess a Canterlot High counterpart, there are some exceptions, or at least cases where no counterpart has of yet been seen while they would have been expected to come up. Most notable of these are Princess Cadance, Shining Armor, Discord and Sunset Shimmer herself.
It should also be noted that the Elements of Harmony appear to be a purely Equestrian phenomenon with no Canterlot High counterpart.
Via these counterparts, most of the Equestrian social hierarchy appears to be projected into a high school and the surrounding infrastructure.
Another interesting fact is that the sirens, who were banished by Star Swirl hundreds of years before contemporary Equestria appear as teenagers amongst the counterparts of contemporary Equestrians.
I can only think of three possible explanations.
One, Canterlot High is in fact a static mirror image of contemporary Equestria. It was that way when the sirens arrived and they, along with the rest of Canterlot High remained that way for hundreds of years until contemporary time.
Two, time passes differently in Canterlot High and might in fact be dependent from travellers from Equestria. That way, only a short span of time passed in Canterlot High between the sirens' and Sunset Shimmer's arrivals. This is however dubious since is it is suggested time in Equestria and Canterlot High pass at a similar rate and constant relation.
A third explanation might of course be that the sirens in their Canterlot High humanoid form possess some sort of immortality. This would allow time in Equestria and Canterlot High to pass parallelly, but would raise some questions on the counterpart system, for example in regards to Celestia and Luna. The problems this explanation throws up makes it quite dubious to me, as well.
Afterthoughts:
It is possible for certain types of magic to pass between Equestria and Canterlot High, even without the medium of the mirror. As such it is plausible for powerful and capable magic users such as Discord or the Tree of Harmony to transport between the worlds without need for it. This might explain how the Element of Magic released Equestrian magic into Canterlot High without the other Elements present to activate it.
It might be possible for Equestrian to bypass the biofilter inherent to the mirror by use of a petrification spell and thereby arrive in Canterlot High with their form and capabilities unchanged.
The fact that Canterlot High contains a counterpart of Equestria within a much smaller and less complex scope as well as some other details like the lack of counterpart and functional magic suggest that Canterlot High is a projection of Equestria onto an information era high school. The two worlds are less alternate versions of one another, it is more that one is the distorted mirror image of the other. I think it considerably likely that Canterlot High is some sort of artificial reality, akin to a pocket dimension, created by Equestrian magic or at least filled with form through projection of Equestria via Equestrian magic. This would explain the counterpart situation as well as the occurence of Equestrian aspects in the case of Canterlot High natives under the influence of Equestrian magic.
Addendum:
This is all I will ever write on that topic. Thank you. It might, however, be expanded in the future if I feel generous.
As always, I will reply to comments, so feel free to do so. If you have anything to add or to suggest, please do so.
The way I always headcanon-ed it was that the world EG takes place in is an artificial construct of extraordinarily powerful illusion magic. At some point in the world's history, a pocket dimension of sorts was created. I had initially thought that it might be to serve as a prison for the Sirens, created by Starswirl, but this presents a few continuity errors. The point, however, is that whoever made the world wasn't powerful enough to create a "true" universe, but was clever enough to realize they didn't need to. I imagine that what occured was the "pinching off" of part of the Equestrian universe, forming a literal pocket, with the only opening being the pinched neck, sealed by the mirror. However this was accomplished, the process effectively "blanked" the inside of the pocket, requiring something to fill it with. That's where the illusion magic comes from, and why the entrance to the other world is a mirror: whatever is reflected in that mirror, on a large, metaphysical scale, is reflected into the pocket, forming a universe populated with constructs mirroring aspects of the home universe.