Rainbow Dash takes part in a Daring Do scavenger hunt and finally finds her goal, a bird skull necklace mentioned to be cursed in the books. Believing that was just for the books, she puts it on...only to find the curse is very real and very fast spreading.

Side note, if you're wondering why her pony wing is rainbow and not blue, it's how the artist draws them on her and I think it looks cooler, so I didn't ask to change it :)

Art by https://marsh-mal-oh.deviantart.com/