As a Pokémon expert, I can tell you that Gyarados, a Water and Flying type Pokémon, does indeed have the ability to learn the move "Fly" in the Pokémon games. However, it's important to note that Gyarados is already a Flying type, so it inherently has the capabilities associated with that type, including the ability to fly.

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Doduo is explicitly stated to be flightless, but can learn "Fly" in the games. Mantine is a dual water/flying as well, but doesn't appear able to fly in the manga/anime/games. To that effect, Gyarados cannot learn the HM "Fly" but it can be taught to use Bounce.read more >>