Teenagers who run away from home to live in the wilderness may become feral. As they become more and more feral, they gain some supernatural powers (a la Peter Pan - ability to fly, things they imagine come true - possibly quite powerful), but at the expense of their humanity and ability to speak, comprehend complex subjects, etc. Maybe they have a leader: the most feral of them all.
A regression into a fantasy childlike state.
As the PCs cross a brigde/tree over a deep river they see the glimmer of gold and jewels lying at the bottom. At further inspection they notice that it is the skeleton of a man still holding on to a sack of treasure. Will the PCs try to dive to get it? What killed the man? Did he simly not let go of the bag he could not swim to the surface with? What cleansed his bones so? Are there flesh-eating beings that dwell in the deep? Can the players resist the chanse of being wealthy for once?