Roaring Moon's name is a direct translation from the Sumerian, for this dragon survived into the very beginning of history. Paleontologists and historians agree that the name refers not to any vocalizations, but to the low and rumbling sonic booms heard whenever it flew by. It is commonly speculated that the sound it made at close range would be a high-pitched shriek, akin to how Yanmega shatters glass. The sources say nothing of this, and historians are divided on whether Roaring Moon was a timid beast who stayed away from Man… or whether any humans who came too close to this pokemon did not survive long enough to inscribe the experience in clay. Strained attempts have been made to connect battles with Roaring Moon to a number of dragonslaying myths, but their descendant, Salamence, is a far more likely origin.
Roaring Moon's wings resemble Ho-oh's, and like those of their legendary counterpart, could hold it aloft for as long as the pokemon desired. Although Roaring Moon could physically land and walk, its diet and the lack of footprints suggest no significant use of terrestrial locomotion, and the ability itself may have been vestigial.
A popular theory holds that mega pokemon represent a return to the evolutionary past, but in most cases the fossil record is too sparse to confirm or deny this, and in Mewtwo's it is of course flatly impossible. This theory is extrapolated from Roaring Moon, and in regard to Mega Salamence's immense wingspan, if nothing else, the atavism thesis is unambiguously true; the legless mega pokemon might fairly be considered even more derived than its ancestor, and even more neatly resembles a crescent moon in its shape.
And yet Roaring Moon are extinct, and Salamence's mega evolution is only a temporary echo of what this pokemon was.
