How can you make a realistic looking mermaid tail for a costume?

You can buy a brand new tail from mermagica.com. They have tails that cost $100 and that is less expensive than some. If you don't really want to spend that much of money, you can make your own. To make your own you need a mono fin that you can buy from Amazon or a swimming store if you could find one. You need a stretchy water proof fabric that you can get from Joanne Fabrics. You need paper, tape it together then draw your tail then cut it out. There are videos on YouTube that show you how to make it. In about a year or month, depending on how much you use it, it can rip or tear so be careful with your tail. You could even try spells, who knows, they might work. That's probably all I can think of. I hope that helped! :)