Pegasus is the name of a specific winged horse. It has no plural.

While the Latin word "Pegasus" references a specific name, the term pegasus is also the name of a breed of mythical creature that frequently appears in various fictional works. When referred to in plural, they are called pegasi. Examples of fictional works that include [i]multiple[/i] pegasi include Fire Emblem, World of Warcraft, Final Fantasy, and various books that I've read over the years. In addition, the very movie OP is referencing includes multiple pegasi, as seen in this image: https://images.app.goo.gl/Yr8WLq8RJwLchT2t5

But given that the "species" is named for a proper noun (and thusly has no original plural form), would it not fall under the English rules for pluralization rather than the Latin, similar to how we call men who play around "lotharios" or "casanovas" rather than "lotharii" or "casanove" as Italian plural rules would dictate?

The works above reference them as "pegasi" when talking about more than one, so that is the basis I'm using. Whether or not the laws of English would apply is irrelevant when dealing with creatures named in works of fiction. If an author/game designer decides to use a non-existent species in their works, the naming of such creatures is their prerogative. Even if we [i]were[/i] to apply English rules, there are scenarios where the plural version would make sense. If you had a room full of people named "David" and you decided to narrate them without simple pronouns (like "they"), you would most likely refer to them as "the Davids" instead of "the David." Of the following, which makes more sense? A) The David have been eating well lately. B) The Davids have been eating well lately. Almost anyone will answer "B." Either way, it makes little difference when you consider that you are referring to the name of a specific creature, a proper noun, and I am referring to the name of a species, an improper noun. Standard nouns are subject to plural rules. horse -> horses mouse -> mice cactus -> cacti pegasus -> pegasi If I was referring to a pegasus named Pegasus, then you would be correct. However, I am not. (Note that the only time the word "pegasus" is capitalized in this thread is the single time I reference it as a name. The lack of capitalization is indicative of my usage of the word as an improper noun.)

But that's exactly my point, it is a common noun that is derived from a proper noun, such as "lothario", "atlas", or "adonis". We don't say "lotharii" or "atles" (and as far I can tell "is" in Greek would imply a feminine form of a word and thusly "Adonis" would be the feminine form of Adon and would not be be pluralized), we say "lotharios", "atlases", and "adonises". Also, as in your example, we say "Davids", not "Davidim" as the rules for Hebrew would dictate. There are also examples of common nouns that are of latin origin that follow English rather than the Latin form such as "stadiums" rather than "stadia" or "climaxes" rather than "climaces". [b] [/b] I'm not saying you're wrong in that pegasi is a plural form of pegasus (it totally is), I'm just saying that it isn't "the" definitive form. It is as you said. A "pegasus" is not a real thing, there's artistic license in the naming convention. It's the same with [i]Game of Thrones[/i] having "dragons" rather than "wyverns.

Oh boy, now we can talk about dragons vs wyverns! Different cultures have different standpoints on this, of course, but in most cases, wyverns and dragons are completely different creatures. Similar to the difference between drakes and dragons, they are mythological 'cousins' of sorts. A wyvern is typically regarded as a two legged dragon-like creature, often sporting venom in a barbed tail or claw. They're both -blam!-ing awesome, don't get me wrong, but from what I've read over the years, they aren't quite the same.

I've always seen it as wyverns are a subset of dragon, similar to how Chinese or Japanese dragons are "dragons" despite not having wings. Like how a lion is a "cat" but a "cat" is is not a lion.