Since your Nincada evolved into Ninjask something else has unexpectedly joined your pokemon team too, it's cocoon, Shedinja.

It doesn't seem to ever breathe nor twitch or move like any other pokemon does, Shedinja's merely an empty shell that hovers a few feet above the ground and follows you and your party around as if it had a will of its own.

This whole ordeal creeps you out, and most of your pokemon share your sentiment as well, but at least Ninjask seems cool with it's "twin."