:D That would be lovely! My hair comes to about my shoulder blades. Would that be long enough?
definitely! first off, dye it whatever color you're gonna want for your costume 12-18 hours BEFORE you do this, it'll make it a lot less messy:
first, if there's even a hint of curls or waves in your hair, flat-iron the crap out of it.
second, find a pillow and an old t-shirt. you're going to ruin it, so don't use anything you'll ever want to wear again. put the t-shirt on a pillow like a pillowcase.
third, get a friend, a hairbrush, a very strong hairspray (got2b glued freeze spray is the best one i've found), and a blowdryer. lay your head down on the pillow sideways and have your friend brush your hair into a fan shape radiating from your ear. once it's ready, your friend will spray the hairspray into 2-3 inch wide sections of your hair, then blowdry it for about 45 seconds to a minute. keep going until that entire side of your head is fanned.
fourth, sit up VERY carefully and turn over to the other side. repeat the process on this side.
fifth, stand up and check it out in the mirror. it will probably be leaning to one side or the other, don't worry, this is easily fixable. take the spray and dryer, grab your hair by the tips and pull it so it's standing straight up, and spray the base of the fan on the side it was leaning to and then blowdry it to set the spray. you should now have a perfectly formed betta tail on your head. it'll look a little something like this:
once it's finished, you can use a can of spray dye to add in speckles, ray stripes, butterflying or any other color pattern you want to add to your betta costume.
NOTE: unless you're wearing a buttondown shirt, you MUST be wearing the shirt of your costume before you start, as trying to put a shirt on over your head once it's done will ruin it. you might wanna practice a few times before halloween to make sure you and your friend get your technique down just right.