Are game mods legal

they are illegal if like some xbox person comes to your house and finds the mods on it

Improved answer: Game mods are not illegal if you are using them to play copies of disks you have already purchased. You have the legal right to make copies (or archives) of software you have purchased so you can use them if needed. If your $100 game gets badly scratched or damaged so you cannot play it, you have the right to use the BACKUP copies you have made --- period. This right has been held up in court legally. No it is not illegal to do if you are using it for the intended purpose.