You cannot copyright an name, logo, or idea. You can trademark a name or logo though.
A copyright allows you to sue for damages, assuming you have any. It could cost you a few thousand bucks to retain a lawyer to do so for you, assuming you aren't one yourself. So unless you're making boatloads of money from your game and are so popular you expect others to profit from copying it, then no. Basically the only main reasonable situation is if someone else sells your game without your knowledge. Do you have a way of finding out who to sue?
If your work is derivitive of Pokemon, you are infringing on Copyright. If you draw a Pokemon that is distinctly recognizable, you are infringing on copyright even though you drew it yourself.
The question to ask is are there enough significant or distinct differences that show it is your original work?
For example anyone can make an RPG about capturing creatures and levelling them up to fight, but I would avoid things like throwing balls to catch them or any sort of electric mouse.
If you happen to make any significant money off of your work and the entity you are copying from is nintendo... Yes I would definitely be worried about getting sued.