In the Abyss, you expect the nature to be hostile and strange. Flesh-eating cobble stones, soil that slowly dissolves you while you walk on it, acidic rain - none of these are too surprising in the Abyss.
Some dangers, though, are more spiritual - like the Lying Rain. It can appear on almost any layer, in almost every realm. Even at a clear sky, the white, almost transparent raindrops fall down on the locals. Strange enough, the rain mostly appears in centers of life - be it jungle or city.
The drops of the Lying Rain never touch you physically. The reason's simple: The drops themselves are not corporeal. They are memories, the last thoughts and emotions of those who died horrible deaths in the Abyss. They have gathered in spiritual clouds of pain and shock, invisible, yet heavily pressing down on the life below. Some of the memories have mixed up, creating new stories that never happened, tales of horror even more stirring and confusing than the original ones.
Whether mortal or immortal, those who come in contact with the drops take these memories as their own, new fragments of their minds that mask themselves as the creature's real past.
The memories all show someone's death, but such a memory doesn't make much death when you're still alive. So, the raindrop-memories adapt, fitting into the other memories of the influenced person. A shy merchant might suddenly remember how HE brutally tortured and killed an innocent elven maiden. A warrior might think of a battle he really experienced, but remember a scene in that battle which, in reality, took place in a Blood War battle the influenced warrior has never seen.
Sometimes, the adaptions are even more twisted: Someone killed by a vampire or other infectious undead might consider himself to be an undead now, risen after the death scene that he remembers. And with belief being power in the Abyss, the poor sod might actually transform into such an undead creature.
Even worse than the raindrops are the rare lightning strikes. Sometimes, the Lying Rain is not invisible anymore. Thick clouds of thunder form above a place then, darkening the sky within seconds. With such clouds, the rain is even heavier than normal, the memories are worse, and everyone becomes soaked in other people's last minutes.
The blindingly bright silvery lightning strikes always hit intelligent beings. While the rain wets everything, buildings, streets and creatures, the silver bolts fill a single soul with the shock of the worst memories.
In most cases, the victims of such lightning strikes have their souls burned to ashes - literally. There's not even a big difference between mortals and tanar'ri - even the fiends get crushed by the sudden mass of pain.
Sometimes, though, a sod is strong enough to survive. He found a way to adapt the alien memories to his own in a way he could, somehow, live with. But in every such case, the victim is totally transformed by mind and soul - and the body follows instantly.
There are legends where a cutter like that transformed into an avenging angel. With all the - to him, real - horrible experiences he made, he devoted his life to the destruction of the Abyss and all of its residents.
It's quite improbable there's any truth in the legends. The only proven sights of such events tell stories of frightening demons, tanar'ri with powers and strength beyond the according "real" tanar'ri. Most of them are just insane beasts, though, and sooner or later the demonic residents kill the annoying danger - or turn it into their pet beast. A few of the silver bolts' victims keep their intelligence, maybe even parts of their sanity, and find their place in the tanar'ri society, respected or at least feared by most of their fellow planeborn.
If they have been tanar'ri before, they usually transform into far more powerful demons, and their old foes and allies often don't even recognize them anymore. In a way, the creatures they were have died, and a new tanar'ri has been (re-)born.