So how do you defeat the dustflier in 358/2 Days?

Fool. Hit it and don't let it hit you.

Pretty much stock up on curas and just go up to it and do a quick combo then hide and let it do its attack and move in. He really isn't that hard but he took me a while because he takes a while to beat. If you wanna use magic I often added a few thundagas because they hit from far away. You have to dodge pretty much all of its attacks because they're strong. If you need to then beat shadows to get hp but I wouldn't recommend relying on that because you can get distracted easily