“Wears the skull of its deceased mother. Its cries echo inside the skull and come out as a sad melody.” – Pokemon Yellow
“It pines for the mother it will never see again. Seeing a likeness of its mother in the full moon, it cries. The stains on the skull it wears are from its tears.” – Pokemon Emerald
You’ll be hard pressed to find a first generation Pokemon fan that doesn’t know about Cubone’s backstory. Aptly called the Lonely Pokemon, Cubone is known for wearing its dead mother’s skull to hide its face and staining it with its tears. Its mother died when it was young and it howls at the moon at night because it misses her. According to Bulbapedia, its original name in the Pokemon Red and Blue beta was going to be Ophon, a play on the word orphan.
If you look for them, you can find some pretty interesting Pokedex entries. Some are sad, some are happy, and some are just straight up disturbing. Go look for more Pokedex entries for yourself because they’re tons out there to enjoy!