If you buy Rated M video games without an ID card, and what will going happen?

The guy will need an ID and stop you.UNLESS you have already bought it and that means they can't do anything about it.

You will have bought an M-rated game without an ID.

they'll first ask for it, and if u say u dont have it on you, then they'll say they cant sell it to you then.
got from personal experience

It depends. Some cashiers won't even ask you for it. If they do ask you for it and you don't have it, they just say you can't buy it. You won't go to jail or anything lol. Just go back with your mom and get it.