If you guys HAVE to make sparkle horses, unicorns, pegasus, etc.:

Go to deviantART or something. This site is homage to SPIRIT: STALLION OF THE CIMARRON. It's based off of books, based out of reality. I highly doubt that a mythological being -- such as a Pegasus (out of GREEK Mythology, mind you) -- would have ANY place in *realistic* Oklahoma/Cimarron Territory.

But I'll reiterate, as I have many times before. If such creatures are so important to you, there are other websites where you can create them. DeviantART has the HorseArt-RPG group where you can create, "show," and even "breed" them against other players. Animation Source isn't omnipresent and certainly isn't the ONLY site you can post horse art on.

Characters need to stick to the movie's form of reality, since no mythical or spiritual things were seen or mentioned in Spirit, they are not allowed as characters. If Spirit learned about Native American mythology while at the camp even if it was mentioned you could use that as an excuse, but alas, it was not.

If Balto 2 never happened I'm sure a lot of the mythical characters there wouldn't be allowed either.

you know im sorry but i agree with luna
i mean we could at least have one spot were everyone could submit their own mythical creation i mean just one spot where you can submit your mythical creations i would love to as i love making unicorns and stufff i've drawn them on paper and one of these days i would like to be able to show all of you but i cant without using my tutorial site. i hope some of the mods see this at least i mean charlie the unicorn had decendants cant we have a spot about him? LOL (though it would kinda suck because ...well... charlie the unicorn does look half as good as the dream works creations) :/

what halt said allso theres going to be a MLP sourse so if you want pegusus's or unicorns or sparkle horses thats where they could go (iv got a fue designed my self)

Note that all of the sources are about specific movies. On each source, they have details about the movie, screenshots, the official characters etc..
So basically they want to keep everything ABOUT the movie. How would creating a unicorn of pegasus stick to the movie? Even fan made characters with out a 'relation to Spirit' are kind of related. None of them are sparkles (like in the movie) and the horses are usually based in the west, are mustangs etc (again, like in the movie).
But creating a unicorn/pegasus/sparkle horse just strays too far from the point of Spirit source - it's not related to Spirit or his world in any way!

I hope this kind of makes sense - i tried to put it in good words XD