Could also be floating. Like those grues.
My personal pet theory is that the monster in the dark is a tiny, tiny fragment of the scrawl, somehow stuck in this world. Not much to base that on, except that could maybe give cue as to how Xykon came to learn of it's existence.
But hey, IF I'm right, I totally get to call out that I knew it, so why not say it?
If I'm wrong we'll never mention this again instead.
Seems the way the story's going they're building up to his eventual reveal, though. But even then, that'll be a while.