I haven't seen anyone post a help topic about this quest yet.
Anyway, I just finished Level 5, got the Flippers and I've been searching everywhere for Level 6 but I can't seem to find it. I looked everywhere in BOTH overworlds (with the exception of one screen in the Light World) and I still have no idea where it is. Could anyone tell me where Level 6 is, or how to get to it?