Okay, I've finally worked up the courage to post this, let's see how it plays out. Writing an -EX has been a goal of mine since I started contributing to the site, and this is the closest I could get — it may not be technically explained, but it's still valid in-universe. I also wanted to write something that was literally just a monster, and a large, carnivorous, nocturnal mammal fit the bill nicely.
The whole thing was inspired by me walking my dog on a field at night, and realising I could only see her through the corner of my eye — this article explains the phenomenon pretty well. In any case, I hope you enjoy my scip about an invisible creature that may or may not exist.