The story goes that a friend of mine discovered this piece of artwork in an old Japanese web archive a year or so ago. Its origins are entirely unknown excepting for the fact that the name ‘Kage no Mushi’ is in its file name.
It art style is similar to that of the other alpha Pokemon starters, while its design bears a resemblance to both Paras and Sewaddle.
The general concept, however, brings to mind the runored PokeGod Shadybug, especially considering the meaning of 'Kage no Mushi.'
I don't think there's anything to suggest it's fake other than it's unknown origins. I remember a few months back someone on a forum mentioned that somebody had beta artwork of either Sewaddle or Nincada and I had been searching for it since. And then this pic turned up on the fuckyeahbetapokemon! blog. I was well chuffed when I read about it. But even if it is fake it looks very cool, in my opinion. And sorry for the long post .
You can notice those subtleties? At least at a glance the artwork seems to share the general of the other pieces in the 'series,' but you're right that there does seem to be some discrepancies. Where do you think the piece would have originated if it were to turn to be fake?