I assume you mean when you fight the first two mutants on the bain drug. Its repitition, and practice of the controls. Try to focus on one, and use your dodge. You can usually get in about 3 to 4 hits, before you have to dodge thier attck. Their charge attack takes the most out of you. Therefore, you want to try and avoid those as much as possible. Remember you can throw a batarang to blind them as they charge, causing them to crash + take damage. Once you damage one enough, climb on its back, and steer it into the other so it damages it. Just avoid their attacks, and get clean hits in, and focus on one, they will go down.