>>40958625Phione is such a weird case, because it's objectively a worse Manaphy mechanically. And because of its extremely odd method of obtaining, you're likely to never use it in any normal playthrough, and even if you did get Manaphy, you'd just use the Manaphy instead, and only breed for Phione as a novelty. Its existence is an enigma, I don't know why they created it in the first place, and while I don't hate it, it's just frivolous.
You can probably call it Mythical, and there's a few official sources that support that (but a few others that say otherwise), but again, it's so weird that it doesn't follow the usual classification for a Mythical. Never given in events, only obtained as a product of breeding a Mythical, and can be replicated through eggs like any normal Pokemon. In that sense, you could probably call it something dumb like a "pseudo-mythical" as the only Pokemon with that classification. Really, what they should do is throw it in a game as a rare wild encounter, and just make it a normal Pokemon. That way, for the first time in its history, you'd actually have a chance to use in a playthrough completely separate from Manaphy.