Fan Theory Time · 6:31pm Apr 25th, 2012
So the season is done and now the summer is upon us (with lot of fun fanfics ahead). But I still see a lot of stuff popping up about Cadance being an alicorn (and the ramifications of her being essentially immortal) Well, I think it's time for fan theories regarding Alicorns... you know aside from the fact that IRL Hasbro just wanted another alicorn.
What we know about Alicorns:
1. Have both wings and a horn
2. May have augmented magical powers
3. Longer lifespans (I'll get to that in a sec)
Lets go back to Equestria's origins. Pre-Equestria, ponies were very separate, only really coming together to work on food. Most likely this meant intermarriage was off the table. However, post-Equestria founding there was likely more intermarriage. As seen in Baby Cakes, pony genetics are host to genetic rarities such as atavisms (thank you Yu-Yu Hakusho for the science lesson). Therefore, I posit that alicornism is a genetic anomaly caused by pony intermarriage.
Now moving on to why Luna and Celestia so special. One word: Discord. I have a theory going that perhaps Luna and Celestia were the first alicorns or part of a subgroup of alicorn ponies. When they went to fight Discord, he messed with them and made those two the demigods they appear to be in the show. He was shown to cause the sun and moon to go crazy, so it's likely prolonged battle with him caused the sisters to inherit that power. Now following his defeat they became rulers. This may have secured them and other alicorns are royal, establishing a royal family so to speak, with only mares being affected by alicornism (Prince Blueblood wasn't an alicorn, yet Cadance was).
So essentially Cadance, being a mare and part of a royal bloodline, is subject to alicornism, but is not subject to the longevity and immense power Celestia and Luna have.
Also, thinking about this gave me an idea for a sad story. What if ponies with alicornism were forced into the royal family? Oh I think a sad tale for Cadance is in store. But for now just have fun with her in Reality Break.
Ha! This makes total sense now! I wondered why Blueblood wasn't an alicorn, yet Cadence was.
I had myself a theory, too, but similar to your own. I think that Luna and Celestia have all three pony type attribute, while Cadence is merely a Winged Unicorn, possesing only wing and horn, without earth pony attributes. kind of a Minor Alicorn. Some Pegasi are huge, and Some Unicorn are, too. Maybe they're erath-Pegasi or Earth-Unicorn hybrids. As for Earth ponies, they'd been shown to run the gamut of size and shape; Genetic variances from the influence of Unicorn and Pegasi bloodlines, maybe? It's fun to speculate on such. And we always have our favorite mixed-bag, the Cakes, to speculate with.
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This is kind of how I view it. Luna and Celestia are both alicorns, which are a really rare combination of an earth pony, a pegasus, and a unicorn. Cadence is actually a pegasus-unicorn hybrid, although at first glance, she looks like an alicorn, and is therefore dubbed as such. Blueblood is a unicorn-earth pony hybrid, not actually a unicorn, but because at first glance he looks like a unicorn, and dubbed as such. Both have really rare mutations, causing them to be hybrids. When hybrid foals are born, they instantly become royalty, because of Equestrian tradition, and are titled 'prince,' or 'princess.'