Dead or Alive 5

This one isn't much of a challenge. From the main menu select the 'Fight' option and from there choose 'Time Attack'. It doesn't matter which difficulty you choose at first, since you will have to go through them all for another achievement, so it's best to start with rookie. Just pick the fighter you are most comfortable with and fight through the fighters. You want to beat 8 minutes, so it shouldn't be so hard. Once you finish all the fighters with a time under 8 minutes, the achievement will be yours.