kenmarable
Hero
Might be fun to start them as the high levels already back in time as their level 1 selves - only due to the "memory fog" they don't realize it yet. They just have a vague but powerful sense of a great destiny or mission they are on. After the first couple/few levels they realize the truth and remember enough to be able to start moving back and forth.
Of course, if you are going with the high levels going back in time to occupy their low level bodies - does that mean the low levels go forward to occupy their high level bodies? Could be some interesting aspects to the high levels (who are aware of what's happening and are trying to fix things) returning to find their very confused low level selves have been causing trouble in the future.
Of course, if you are going with the high levels going back in time to occupy their low level bodies - does that mean the low levels go forward to occupy their high level bodies? Could be some interesting aspects to the high levels (who are aware of what's happening and are trying to fix things) returning to find their very confused low level selves have been causing trouble in the future.