EmporerDragon has a great solution, but for some the achievement may glitch out due to how the game requires the user to sign-in during the game. If the glitch happens and you are stuck at 98-99%, you can still get the achievement, but it will require some major replaying. To get the achievement, you must delete your save file from all sources (restarting the game from scratch) and must unlock all the characters again. Deleting the save file resets the progress of the achievement in the Achievement App, which makes you have to redo all the combos again, and since the save file is deleted, most of the characters are locked. Hopefully this doesn't happen to anyone like it did to me, but this is a decent fix if you are a completionist.