Excerpt from the Equestrian Archives:

'Sunburst, a unicorn scholar and vice headmare of the School of Friendship, is best remembered for an unfortunate incident in which one of his spells accidentally transformed his body so that it was made out of latex. Though he was still able to breathe, sleep, and perform all other normal bodily functions, he lost his ability to cast magic, as well his ability to speak. As expected, this was highly embarrassing, and led to a long period of depression and melancholy when numerous tests revealed that the effects of the spell were permanent and irreversible.

Unable to change back to the way he was, Sunburst eventually dedicated the rest of his life to studying irreversible spells and managed to discover several cures, saving countless other beings from suffering fates similar to his own.

It is worth noting that a modified, non-permanent version of the spell that changed Sunburst became extremely popular, and remains in wide use today.'