There are many jobs available in Miitopia. Every job has different powers and different abilities.
Default jobs for the first world:
Jobs unlocked after clearing Greenhorne
Jobs unlocked after clearing Neksdor
After every area, the Dark Lord seals away the players powers and you have to choose a new job.but after clearing the Realm of the Fey the players powers are still there because they were "too strong".
In Karkaton, right before the volcano, the player and their party members will become able to change into any job of their choice, so you can turn into a job that the Dark Lord sealed away. A Mii's old jobs' progresses will be maintained. The jobs that the Dark Lord had sealed away also keep their progress from when they were sealed.