In ancient times lived a mage of tremendous power who sought the assistance of an apprentice for magical experimentation. Through trial, he found that no worldly mortal could endure the gruesome nature of his experiments, much less their horrifying results. He needed someone strong enough to tolerate his experiments, but who would obey his every word. For his solution, he looked to the planes.
He began his expedition from the quiet of his laboratory in the Western Realms in search of the mystical formulae and articles he would need to summon the extra-planar beings which he would have do his bidding in the world. His quest was years long, spanning from his home in the Western Realms to the Land Atop the Wall. However long it took is unknown. What is known is that he was successful. Some would say too successful.
During his journey, he was able to complete the formulae for his spell and gather all the objects he needed, the last of which was water. Not just any water, but water from the fabled Well of the Planes, which he found among what is now called the Hills of Black Lightning. So overjoyed was he about his discovery that he cast his spell before even examining the water he got. This was his only downfall, for what he didn't realize was that there exists among the hills seven wells, for seven correspondingplanes. that which he took came of the well of the Abyss.
Now, if you are in the Hills of Black Lightning, it is said that if you call his name, he will appear and hand you a copy of the spell!