How do you get into mahogany gym? - Answers

First, you go up north to the Lake of Rage and fight a red Gyarados. You have to have something that can use surf so you can swim to it. Then, press 'a' and battle it. After you finished the battle go back to shore and a trainer named 'Lance' will talk to you. He runs and asks for help. Go back to Mahogany Town and go to the building with a grey sign that says 'no suspicious activity or something or the other (press 'a' to read sign). He tells you to help him fight Team Rocket, so do that and beat everybody. When you finished and Lance gives his thanks, go back to the gym. You should be able to get through.