Weird analogy that came to my mind in connection to MLP:
Angels have wings and devils have horns.
Nah, I'm sure it's coincidental, but an interesting coincidence nonetheless.
Let's continue this line of thought just for FUN:
heavenly: loyalty, pushing personal limits, trying to be your best, inspiring people | loving kindness, compassion
earthly: hard work, honesty, family | having a joyful time, cheering people up, faith
evil: magic, rational thought, science | worship of fancy stuff, fame and superficiality