Every now and then, a mysterious ship drifts emptily into shore, showing no signs of struggle or damage to account for the mass disappearance of their crews. All on board are typically never seen again, and society reckons them to be among the dead, but the truth is far stranger.
These ships have been boarded by Jellicent, who absorb the crew with their vast size in their permeable bodies and dive vast distances to the bottom of the sea. The men (and rarely, in more recent years, women) on board are protected inside the Jellicent's body for the dive, and spend this time breathing the air within these pokemon and slowly adjusting to air pressure through the Jellicent's mysterious power.
When the sailors reach the bottom of the ocean, they find not the dank, formless voids which radar and submarines have thus far discovered, but a vibrant sunken city lit by undersea vents. The buildings are composed of sunken ships and other flotsam, shaped by tentacles into rounded architecture, and the entire city rests beneath an awesome Jellicent-shaped dome. Here, the discarded sailors bring their human technology, giving these intelligent pokemon everything from poke balls to maps and compasses, although they can only offer what is in their pockets and what they can reconstruct from memory.
Many of these sailors live happy, full lives in their new homes, the sorrow of separation from everything they know in time replaced by the wonder and new joys of the undersea Jellicent world. A few, however, become homesick, and fewer still journey home; those who succeed at this escape must perform a feat rarely paralleled in human history. Should they return to shore, they are often mistaken for imposters, and always considered mad whenever they tell their bizarre story.