If you are making a multi-colored mane or tail like those of Rainbow Dash or Twilight Sparkle, you will need 1/8 yard for each of the "accent" colors. (All 6 for Rainbow or Fuchsia and New Purple for Twilight.) The strands will be cut on the crosswise grain instead of the lengthwise grain though, so they are more prone to stretching out if tugged on.
That should cover everything, but if you have any questions feel free to let me know.
And if you scrolled through this entire post wishing that you could sew-along but thinking to yourself...
"But I don't even know how to sew a button!" or "I'd really like a costume, but I just don't have time to make one."
Please stop back tomorrow for a special Etsy shop announcement!
Ok, so who's going to sew-along with me?
I can't wait to see a whole herd of little ponies!