Ah, good ol' Cubone. For years, this little guy -- a member of the original 151 Pokemon -- was commonly regarded as the ultimate in terms of depressing origin stories
"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. It wears its mother's skull, never revealing its true face".
it cries because it misses its mother. It misses its mother because she is dead. And even worse, in the original games, you can actually encounter the ghost of a Cubone's mother (a Marowak), that was killed by Team Rocket. Killed! By Team Rocket! Looks like someone didn't prepare for trouble.
There is a bright side, though: By the time you level it up to Marowak, the Pokedex informs you that it "has grown tough by overcoming the grief of losing its mother. Its tempered and hardened spirit is not easily broken." Motivated and toughened up by the death of its mother? Hardened spirit? Dishes out savage beatings to others? Guys, that is basically Pokemon Batman.