They come by infernal and Stygian IRT subway

stygian darkness

Everyone has an air of déjà vu about them, and they float like shadows over the waters of the Styx.

A few inveterate smokers went out into the waiting room, but returned at once, driven back by the Stygian darkness.

she and Sam made their way down a Stygian stretch of Amsterdam Avenue

Bathed in this warm glow, a young woman named Ashli lay sleeping, impervious to the stygian immensity of her surroundings