Do you want a shiny megagengar??
Don't worry, I've cooked with methylamine a shiny gastly just for you.
In particular, this is a Timid 31/x/31/31/31/31 shiny Gastly. No nickname, no egg moves.
What I'm after? Pinsirite, Tyranitarite, Mewtwonite X, Manecticite.