Critter of the day: Glitcher
Glitchers are supposed to be scary and unsettling. I imagine they move around like Clickers do in The Last of Us. I mostly envisioned them for TL6 and forward games, as a result of failed time travel/teleportation experiments, but they can very easily be re-skinned to adapt to other themes. Their attack is unlikely to bypass much of the armor usually worn, which can lend to a false sense of security... until a player takes 4 points of injury outright to a failed HT roll.
Tune their Terror penalty to taste and scare players away!