Krashface

Also, even if the comics aren't canon, Sombra isn't a common unicorn. He is a Umbrum transformed into a pony, so basically his origin isn't organic, but rather of pure dark magic, making him closer (if not even more powerful) to Twilight. But of corse, this isn't totally canon, unfortunately. And the fact of having a broken horn is something exceptional ! This said, the horn of a unicorn function more like an amplifier and channeler , rather then just a bone protuberant . Given the nature of the show, is even understandable, but one may immagine what spells have been created, in older and more perilous times, and in greater stories (I really hope the next gen will show something more of how magic can be used to fight ).

Finally someone starting this Ok, Long post ahead. Ok, let's see: as I immagine, Magic is some kind of force that can channel into a pony, but sometimes, for unknown reasons related to bloodlines and luck, some individuals can manifest the power to manipulate and create magic. This said, Twilight's abilities and affinity with magic are more of a natural gift (and producers decision ), but as anyone who've followed the series till now, others have manifested incredible talents with magic. And with this, I mean Starlight, just for start. As you said, @Sagely Thyme, the possibility that a unicorn (or a non-unicorn) may become even more powerful than a Alicorn is possible, although remotely, since this horned and winged creatures are the concentration of the three major races of ponies. And about the question about challenging an alicorn: Celestia and Luna's magic is releted to stars, so something incredibly powerful even to master, and I barely think that, without cheating, some pony may beat them, let's not speaking of Twilight who's "element" is magic ! But as we've saw, and @Midnight Seashell rightly implied, the existence of artifacts of some ancient times (even more then 1000 years?) can grant a pony or even, who knows, a strange monkey like being to command nature itself. Even if in some cases, the artifact itself need magic to work, first, like the Storm Wand of the Storm King. And this concept, of stealing magic for incrementing the one someone may already possess, is very well depicted by Tirek, who got strong enough to challenge Twilight. Oh, and the Alicorn Amulet... possibly, that thing isn't just enchanted, but rather cursed, and will slowly transform a pony into it's creator ( chilling, man) This said, the ability Twilight have with magic is probably something related to been an Element: she have been chosen by Magic to be its vessel, and so she can manipulate it with ease, and becoming an alicorn made her even more powerful. Althrought not the most powerful. I don't know if Flurry will loose part of her powers, once grown up, but I think that a pony born Alicorn is something that goes over comprehension: she already manifested and OP power, but hey, maybe she'll get nerfed . But if the magic we are speaking about is the "light one", what about dark magic? Sombra demonstrated, and Celestia explained, that this type is more powerful, yet unstable one, and what I always imagine is that that magic can be easely used by anyone who can manage to channel magic, but at the price of the user's sanity. I'm gonna admit that I'm really interested in this one, since it seems that is rather... alive, like the Umbrum or the presence that transformed Stygian. May magic actually manifest, if it had the opportunity ?

Probably I'm waaay too late with this, but what about Hollow shades and the Well of Shade ? I hope the developers will include the place in season 8, and possibly some explanation for why such a strange place exist, and what, in the past, happened in there.