https://makesweet.com/my/flag will take you to a website that lets you create a flying flag. create a flag, press "insert photo" then find the place you saved it, usually in downloads. once you do it, you'll just get a picture. then click the clapperboard (all the way to the right, the thing you see at the start of a deleted scene). then click .gif, and it will animate. you can then after a few minutes click the clapperboard and a save-disc icon, in which it will start downloading your design. then you get this after you upload it into sprites, not costumes. (you'll have to swap around a few costumes if you upload it to costumes and not sprites)