Done! I really like how this turned out.

INCOMING HEAD CANON:

General:

So the way I figure it, there’s a lot of interbreeding between unicorns, pegasi and earth ponies. There’d have to be, otherwise they’d all die out! And I also think that each race of pony has a different affinity with elements and magic. Pegasi are all about the air, obviously. A purebred pegasus (Like Rainbow, for example) will have a very strong affinity with the air and the magic inherent in it. They’ll be lighter- and I think that pegasi must have thinner/lighter bones, like a bird. I also think that there are different breeds of pegasi. Rainbow, for example, has some hummingbird-like wings- it’s why she’s so fast! Other pegasi might have different wing types which makes some stronger at different types of flying than others.

Earth ponies obviously have an affinity to earth. It’s part of why they can manipulate things with their hooves so well, and a purebred earth pony (like AJ) can do some pretty amazing things. (Didn’t you ever wonder how she’s so strong and can kick down just the apples in an apple tree?) There’s different breeds here too, obviously. I think that the Apple family has a lot of clydesdale-like blood in them. It’s part of why AJ is bigger than Pinkie, for example. She’s bigger and stronger than an earth pony that might be primarily arabian based, but not as fast.

Unicorns are all about that ethereal element of magic. I think a unicorn’s horn size might also have an effect on the potency/control of their magic. A unicorn with a long, narrow horn will probably have more control than one with a short, thick horn- but not as much power. I also think unicorns are different in that for the most part, a purebred unicorn (like Twilight Sparkle) will be frail physically. I think doing magic must take a lot of energy, and so most unicorns end up with slim/slender bodies as their metabolism goes towards fueling their magic.

That said, there’s also interbreeding to talk about! Of course all the different races can interbreed, which of course leads to all the different kinds of ponies we see in the show. An earth pony and a unicorn that interbreed might produce either an earth pony with strong earth magic and maybe an affinity for more delicate work. Or they could produce an unicorn that has an affinity for earth magic along with their inherent magic. (Like Rarity!) A pegasus interbreeding with an earth pony might produce an earth pony that has an affinity for quick movements or air magic (Pinkie!) or a pegasus with an affinity for earth magic (Flutters!).

Pure alicorns (like Celestia and Luna) are a perfect blending of the three tribes. Ascended unicorns are primarily what their race was before they ascended- so Twilight’s primarily unicorn, and Cadance is primarily pegasus. If an earth pony were to ascend, they’d still primarily be an earth pony.

Of course there’s also taking into account all the interbreeding that happens way back in bloodlines to contend with, too.

Applejack

AJ BEST PONY. *Ahem*. As I said, I think that Applejack has a bunch of clydesdale blood in her. We’ve never seen her parents, but guessing from Big Mac, we can probably guess that at least one of them was a big work horse type. She’s one of the taller ponies in the mane six. She’s almost as tall as Twilight now that she’s ascended! She’s also got a lot of muscle both from working on the farm and from being a purebred earth pony. She’s very in tune with both her body and the earth.

Pinkie Pie

I think Pinkie’s definitely got some pegasus blood in her somewhere! She’s always zipping around and she has some… weirdness when it comes to movement. How can she stay in the air so long when she jumps, otherwise? She’s a lot shorter than the rest of the ponies- the shortest of the mane six, in fact! But she’s squishy and bouncy. Partly from her work at the bakery, and partly because she’s a party pony! I think her fur changes to downy feathers in some places, like on her shoulders. If we could see her tail better, she’d also have tiny, vestigial flight feathers right in front of her tail.

Rarity

Rarity is part earth pony for sure. I don’t think we’ve ever seen a horn on her dad, so I think he’s an earth pony. It explains her talent with finding gemstones! She’s got a way with earth magic- not in the way that AJ does, obviously, but in a way that’s harmonious with her innate unicorn magic. She’s tall- almost as tall as Twi, but not quite as tall as AJ. She’s also very elegant and slender- but her fur is coarse thanks to her dad’s genes. I think she’s self conscious about it and that’s why she spends so much time dealing with her mane. (And also why Sweetie Bell is a little round stout thing!)

Twilight Sparkle

Before she ascended, Twilight was a purebred unicorn. She wasn’t as tall as she is now as an alicorn, but she was still a lanky thing. She’s always been a little weak, physically. Being in a library all day isn’t exactly conducive to being strong, physically! And on top of that, she’s always had very strong magic. Her horn is very long and thick- not as long as Celestia’s or Luna’s, but very, very close. Her new wings are pretty generic- something like your standard jaybird type wings. She’s the tallest of the mane six now that she’s ascended. Before, though, she was a tiny bit shorter than Rarity.

Fluttershy

Fluttershy is part earth pony. She’s got a very strong affinity for earth magic- moreso even than her affinity for air magic. Her wings are something like an swan’s wings- good for gliding, but not so good for speed; her flight feathers near her tail are short and not great at helping steer. Despite her earth pony blood, she’s not very strong. She does have some muscle from working with her animals, but she’s not even close to as strong as AJ or Pinkie. She’s not very tall, but she is very slim, and her swan leanings shows in her general looks. She’s in the smack middle for height.

Rainbow Dash

Is 20% cooler. She’s also a purebred pegasus! Her wings are very hummingbird like- she’s fast and has a lot of control. She’s also the lightest (but not the skinniest) of the mane six- her body is almost all muscle. She has very little fat because her metabolism is super fast due to her hummingbird influences. Her flight feathers near her tail are very articulated and help her steer in the air. She’s second shortest- still taller than Pinkie, but not by much!