Basically what you should do is read the licence, this should clarify most doubts.
You aren't allowed to download a GPL game and distribute it with another licence (this is stealing) unless all the code belongs to you, of course what was released as GPL will still be around as GPL and anyone is free to take the project.
Basically if you use GPL code you are meant to release it and all derivative works under the same licence and in the same conditions you recieved it (this means including the source and the same rights).
There is no reason you can't profit from GPL (many do) you can charge for downloads, compiling, support, recieve donations. But you must realize you can't deprive others from the rights you were granted by the GPL. So anyone can copy or distribute "your" code for free or a fee.
Basically GPL is two things, on one side it grants the user the right to access the code and modify it for their own needs and on the other hand it prevents unscrupulous people from stealing this code and locking it up.
So remember if you base your game on GPL code, all the code you add will be GPL as well
You aren't allowed to download a GPL game and distribute it with another licence (this is stealing) unless all the code belongs to you, of course what was released as GPL will still be around as GPL and anyone is free to take the project.
Basically if you use GPL code you are meant to release it and all derivative works under the same licence and in the same conditions you recieved it (this means including the source and the same rights).
There is no reason you can't profit from GPL (many do) you can charge for downloads, compiling, support, recieve donations. But you must realize you can't deprive others from the rights you were granted by the GPL. So anyone can copy or distribute "your" code for free or a fee.
Basically GPL is two things, on one side it grants the user the right to access the code and modify it for their own needs and on the other hand it prevents unscrupulous people from stealing this code and locking it up.
So remember if you base your game on GPL code, all the code you add will be GPL as well