"The Clipper (Parthenos sylvia) is a species of nymphalid butterfly found in South and South-East Asia, mostly in forested areas. The Clipper is a fast flying butterfly and has a habit of flying with its wings flapping stiffly between the horizontal position and a few degrees below the horizontal. It may glide between spurts of flapping."
At first I was thinking about Fighting-type, but when I saw this... that sounded very close to it's name (which I thought it was something like "silvia"), especially to how it's bows are shaped. So now it's starting to make me think that it's a Bug-type.
But y'know what I find strange? Every Bug-type Pokémon design that I've seen is based off either an insect, arachnid, crustacean or arthropod. If Sylveon was to be a Bug-type... it would break the cycle of all Bug-type Pokémon being based off insects, arachnids, crustaceans or arthropods. But again... it doesn't seem likely that Game Freak would develop a Pokémon to be a Bug-type when it doesn't appear like an Insect or something similar in any way.