Apparition in Northern Eavinid

Firsthand account of an unknown anomaly reported in the remote village of Spellstow, Kingdom of Eavinid.  Submitted to the Main Temple of Idikai by Flathac Anotor, year 1353 of the Age of Knowledge.  Additional notes by the author included for the purpose of comprehension.

I arrived in Vistawharf on the evening of the 23rd day of Flarent, at which point the man had been locked up alone for 21 days.  The village elders told me it was "for his own safety" though no one had been checking on him more than to ensure he had food and water.  It took some time to convince him that I was actually there in the room with him, and for him to begin speaking to me.  I had to ask a few times for him to describe what had happened.  

M-my name is Raen. It was the night of Full Dark when I saw it.  I w-was out in the high foothills of the Northern Blades, some friends and I were hunting Peldroms.  They are a bit skinny right now, but we needed the meat.  We'd been out for a couple of days.  I-I had the trail of one, had been after it for a while.  The others wanted to start back to Spellstow, but I knew I could get this one.  I wanted to be a hero.  
He broke down here, kept sobbing the word hero over and over.  When he came out of it, his entire tone and manner had changed. He jumped up and began pacing, whispering to himself and then laughing.  This went on for a few moments, before he turned to me with a wide, rather alarming smile.
You want to see it, don't you!  I could take you to it.  They don't want me to, but I can.  Yes!  I can take you to see it, so it can see you!  You can't have it.  It's mine!  Mine!  But you can see it if you want!  
I asked him to describe what he had seen, and after a few more moments he seemed to calm slightly, though his tone kept switching between subdued, almost frightened, and loudly maniacal.
I followed the Peldrom past the edge of a meadow, up against the face of the rock.  There was a cave, and I thought maybe it had gone in there.  I-I followed it in, but wish I hadn't.  I did!  It was beautiful!  Inside the cave it was dark and narrow, I couldn't see anything.  I went on a little more, and was about to turn around and give up when I saw some light coming from up ahead.  So pretty!  Swirling, talking to me!  I told it everything!   The cave widened out suddenly, like a room.  In the middle of the room was- was-  
At this point the manic excitement took over completely.  He was screeching, jumping onto and off of his bed and running wildly around the room, all the while staring at me with a near frightening intensity.
The lights!  the dark!  They swirled, they ran!  They danced and beckoned!  I went to them, went into them, they went into me!  I am the lights now!  We shall all be the dark, and the lights!  It is here to devour the world!
I left shortly after this, as his screeching became incoherent.  I am still not sure what the man saw, but I shall endeavor to go find the cave he described.