There are two new monsters in The Lightless Depths. One is called a Brain Collector (or Nehthalggu I guess), and is described as being "A hungry polyp upon twelve insectoid legs. Larger than a horse, the thing's tumid mass writhes with whipping tentacles. It has a lipless mouth heavy with protruding row of dagger-teeth, and a ridge of four bulging eyes above. A cluster of twelve knots crown the abomination's misshapen fom, the gray wrinkles of brains trapped within pressed against the semi-transparent membranes." It's a Large CR 7 aberration and can use the brains it captures to apply metamagic like effects to its spells (cast as a 6th level sorc.) without increasing their spell slot level. It can also store more spells known in the collected brains.