Basically, I had a Gengar named NightShade. Gengar is my favorite pokemon, and NightShade was the best Nickname I ever came up with.
I look at it, its name was reverted to Gengar. I try to change it back to NightShade, it says "The requested nickname is not permitted"
This is legit the most frustrated I've been, and I've been through a lot on this game.