Frustration in Excelsis 
Worldbuilding Addict
A semi-random collection of stuff and headcanons:
Equestria's world sits in the middle of a classical geocentric star system. Besides the planet itself at the center, there are the sun and moon (each about the size of our own moon) that move in the same orbit, then a spherical cloud of mobile stars that can be moved and arranged by beings on the surface, and then the sphere of the immobile stars delineating the outer border of the universe.
There are multiple variants of constellation beasts such as the ursa majors and minors, including such things as cygnuses, canis majors and minors, scorpios (mostly desert dwellers), aquilas (typically found in high and isolated mountains), leos (most common in, but not restricted to, the zebra homelands), etc. There are also numerous marine species, such as piscii, capricorns and the mountain-sized cetuses, the biggest creatures found anywhere, but like most other things found in the world's oceans veruy little is known of them. They're more common is some places than in others, but they're always very rare. While they breed as flesh-and-blood creatures do, if much more seldom, they are thought to have originated from stars and wild magic that fell to earth from the heavens, and indeed such events have on occasion been known to be shortly followed by the appearance of a new constellation beast in the area where they occurred.
The rarest kinds of all are those resembling sapient species, such as dracos, tauruses and arieses, who are sapient themselves and typically lead isolated lifestyles in the wilderness, far from civilization (of course, this means that the differences in the habits of, say, a draco and a dragon are minimal at best, the only difference being that dracos do not gather hoards).
The moon is habitable, although very barren. It has literal, shallow lunar seas and is home to its own organisms -- it's actually where the first star spiders came from*. It's also home to star beasts like those of the planet below it, which according to Princess Luna are more common there than on the larger world.
The Equestrian conception of what creatures count as chimeras differs quite a bit from ours. A typical pony would not actually consider a manticore, for instance, to be a chimeric creature -- they would not understand it as a lion with a bat's wings and a scorpion tail but simply as, well, a manticore with a manticore's wings and a manticore's tail. They do sometimes describe such beings in chimeric terms (such as Twilight's description of hippogriffs), but this is more like a human describing a platypus -- it's understood more as anatomical coincidence than anything else. Those creatures that they do see as chimeras tend to be much more obvious in consisting of parts of different animals jammed together (think of the actual chimera from "Somepony to Watch Over Me" -- there's very clear lines where one animal ends and another begins, whereas a manticore's or hippogriff's anatomy and coloration are much more even**). More than a few such chimeras originate from Discord's first reign, although others trace their descent to other occurrences of uncontrolled magic, the experiments of powerful wizards and spirits and other such events, while others are as natural as anything really is in such a high-magic world.
A similar thing goes for what they consider to be "magical creatures" or "monsters" and what are just normal (if sometimes big, weird or aggressive) animals. The simple presence or absence of magical properties doesn't cut it, not when a significant portion of the world's sapient inhabitants can also wield magic in some form or another. Generally, things like tatzelwurms, manticores or hydras are seen as just oversized and weird-looking but otherwise perfectly natural wildlife. Any pony with a talent for working with animals can deal with them, as with Fluttershy and the manticore in the pilot. The reason Fluttershy couldn't do anything about the hydra is because it's more than similar enough to dragons to trigger her phobia. Those things that ponies think of as truly magical creatures are much more obviously unusual or supernatural, such as timber wolves, ursas and windigos.
* This part comes from the very talented"[Carabas":](https://www.fimfiction.net/blog/598821/part-18-of-the-palaververse-the-local-cosmos-also-art-and-thunderstorm) on Fimifction, whose stories and worldbuilding I highly recommend.
** Dare I say, more_*harmonious_* ;D
Equestria's world sits in the middle of a classical geocentric star system. Besides the planet itself at the center, there are the sun and moon (each about the size of our own moon) that move in the same orbit, then a spherical cloud of mobile stars that can be moved and arranged by beings on the surface, and then the sphere of the immobile stars delineating the outer border of the universe.
There are multiple variants of constellation beasts such as the ursa majors and minors, including such things as cygnuses, canis majors and minors, scorpios (mostly desert dwellers), aquilas (typically found in high and isolated mountains), leos (most common in, but not restricted to, the zebra homelands), etc. There are also numerous marine species, such as piscii, capricorns and the mountain-sized cetuses, the biggest creatures found anywhere, but like most other things found in the world's oceans ver
The rarest kinds of all are those resembling sapient species, such as dracos, tauruses and arieses, who are sapient themselves and typically lead isolated lifestyles in the wilderness, far from civilization (of course, this means that the differences in the habits of, say, a draco and a dragon are minimal at best, the only difference being that dracos do not gather hoards).
The moon is habitable, although very barren. It has literal, shallow lunar seas and is home to its own organisms -- it's actually where the first star spiders came from*. It's also home to star beasts like those of the planet below it, which according to Princess Luna are more common there than on the larger world.
The Equestrian conception of what creatures count as chimeras differs quite a bit from ours. A typical pony would not actually consider a manticore, for instance, to be a chimeric creature -- they would not understand it as a lion with a bat's wings and a scorpion tail but simply as, well, a manticore with a manticore's wings and a manticore's tail. They do sometimes describe such beings in chimeric terms (such as Twilight's description of hippogriffs), but this is more like a human describing a platypus -- it's understood more as anatomical coincidence than anything else. Those creatures that they do see as chimeras tend to be much more obvious in consisting of parts of different animals jammed together (think of the actual chimera from "Somepony to Watch Over Me" -- there's very clear lines where one animal ends and another begins, whereas a manticore's or hippogriff's anatomy and coloration are much more even**). More than a few such chimeras originate from Discord's first reign, although others trace their descent to other occurrences of uncontrolled magic, the experiments of powerful wizards and spirits and other such events, while others are as natural as anything really is in such a high-magic world.
A similar thing goes for what they consider to be "magical creatures" or "monsters" and what are just normal (if sometimes big, weird or aggressive) animals. The simple presence or absence of magical properties doesn't cut it, not when a significant portion of the world's sapient inhabitants can also wield magic in some form or another. Generally, things like tatzelwurms, manticores or hydras are seen as just oversized and weird-looking but otherwise perfectly natural wildlife. Any pony with a talent for working with animals can deal with them, as with Fluttershy and the manticore in the pilot. The reason Fluttershy couldn't do anything about the hydra is because it's more than similar enough to dragons to trigger her phobia. Those things that ponies think of as truly magical creatures are much more obviously unusual or supernatural, such as timber wolves, ursas and windigos.
* This part comes from the very talented
** Dare I say, more