If I make a Game and build in a Easter egg about Pokemon or any other Game, can I get Copyright Issues with that or does nothing happen?
It depends on how you create the references. If you use someone else's artwork, yes, you can have a problem. It doesn't look like the main aspect of your game. I believe there's still a possibility that you can use the references. In general, you cannot use a character commercially from another author because copyright laws protect the character, unless you get the permission from the author. However, it's still possible to use the "fair use" aspect of the laws. It's a gray area where lawyers don't even share the same vision. I've seen many references to other characters in the cartoon "The Simpsons" for a few seconds only as a joke. Generally, that doesn't create a problem, but if you start using the character as a pivot in your game, you may get a letter from lawyers' author about copyright infringement. I'm not a lawyer and it's always better to consult a lawyer expert in copyrights. I doubt that you'll get a clear answer to that. Laws are not mature enough to prevent completely that kind of problem. You might be right and still get a lawsuit.
As a rule - don't do it. It's all very well saying "you can claim fair use" - first you'll get a "cease & desist" from the copyright owner's lawyer. You'll reply, waving the "fair use" flag, which is not going to appease them in any way whatsoever. Are you prepared to spend thousands of dollars in legal costs to get your "fair use" when the Copyright holder sues you? Yes you can claim your costs from the complainant IF you win, but in all probability you won't, and unless you've got more money than you know what to do with, a lawsuit like that would probably finish you. In either case you'd need to pay your legal costs up front and I guarantee that The Pokemon Company (for example) has much more money than you do. So forget the fair use thing. Just don't do it. It isn't worth the risk, the cost, the time or the hassle. (and yes, it *does* happen. It happened to me when I accidentally stepped on the toes of a registered trademark that I didn't even know existed).