[ml1201]

To add into the 2-d side scroller, I've played a lot of MegamanX (literally just the first one) and that did actually (save for I think only two bosses) Allow you to travel from the beginning of the stage to the end of the stage and then travel back to the beginning, but mobs would re-spawn from doing so, which would allow farming for stuff (in this case health, energy and life).