This is sweet! Very wallpaper-esque. What's with the floating head next to the tornado?
That's a Screamer. It lives in dark places like caves and dungeons and hates sunlight of any sort. It attacks by screaming incessantly, dealing damage to the entire group and causing the 'shaken' ailment. It can also cause confusion and paralysis, but that's a lot rarer. It has a CR of about 4 or so in D&D, and we may see it in the comic someday as well.