An ethereal plane between the living and the dead. A snake-like tunnel (think Finding Nemo's EAC).
Coral stalks covered in shark teeth forms the barrier that keeps the departing souls on track to the Netherworld.
It is filled with a thick, slick kelp forest, limiting your vision.
The departing souls that float down the stream are those that died without a proper burial and therefore did not pay Charon.
So they must float for a hundred years, slowly losing their connection to their past life and go mad. Attempting to break free of the stream, they become frantic. DC8 to avoid being grappled by one.
If grappled, the soul will head to the closest edge and tries leave with grappled object (PC, NPC, Treasure, etc)
We were clearly warned: DO NOT EXIT THE SLIP STREAM.
No living creature can enter the slipstream, just as no dead can leave.
Doing so = Lost to Davy Jones' Locker, blind and lost to the Void. The only thought it has is :
Join the living once again by consuming the living.
This FALSE hope drives the soul forever until it is destroyed - leaving behind the universe's energy in the form of ASH.
They come from the deep, a SCOURGE against the natural world, bringing with it an abonanational infection