A yamask is a spirit of a human who died and then was reborn as a ghost-type Pokémon. So this would indeed be me in the Pokémon world, I probably got myself killed by some Pokémon. This Darkling is dark grey like a normal yamask, has a silver mask like a shiny yamask, and has green-eyes because I thought that would be more fitting than red eyes like a normal yamask or yellow eyes like a shiny yamask. She wishes she could evolve but she can't, because she once accidentally ingested an Everstone (which prevents Pokémon evolution), I thought of a sort of headcanon thing that since she has a silver mask like a shiny yamask, she would eat a little silver occasionally to maintain it, while a normal yamask would eat a little gold occasionally to maintain his or her golden mask. So this scatterbrain basically mistook the Everstone for a piece of silver. And now she will be stuck as a puny wisp forever. Because although Cofagrigus is tied with Yamask as my most favourite Pokémon, I don't think a Cofagrigus would represent me as well as a Yamask.

Maybe I should have written more here about my actual reasons for choosing a Yamask as a 'sona, and why I think it suits me. Because I do have explanations I could write, I just have to think of the right way of writing them. I will another time... sometime... if I remember...