[Theory] Drastic dark areas?

[Damascus]

It would be fun to make a custom story where the darkness is alive and malevolent. Out of the corner of your eye, you see a shadow in the corner that is abnormally dark for the lighting in the room. And as you watch, it becomes darker and darker, and begins to grow out from the corner. Soon it is pitch black, and coming toward you. You try to run, but when you get to the stairs that lead to the first floor, the bottom of the staircase is enveloped in the same impenetrable darkness. And it comes toward you.

Is it possible at all with the HPL2 engine to achieve some sort of effect like this? I'm imagining it two ways: first are Lights that cast shadows instead of brighten an area. Second are invisible objects that cast shadows, but the shadows wouldn't nearly be dark enough.

This is just a random theory I'm throwing out there for any super advanced programmers out there who might have any ideas.