James Jacobs wrote:
There's 666 layers of the Abyss because 666 is a spooky number.
Allow me to be a neigh sayer.
Why would the formless, infinite expanse of the Abyss be limited to arbitrary hard-set rules like having 666 layers?
That and I always associate 666 numerology with devils because of the background for the number and the themes and names of D&D's devils, with only the 1e use of 666 layers to the Abyss linking demons to it.