Neh-thalggu

A brain collector, or neh-thalggu in its own speech, has a swollen, greasy, shapeless yellow-orange body fringed with dozens of short squirming tentacles and carried on six crablike legs. Its bulbous head holds four big bulging yellow eyes, a fanged maw, and up to twelve lumps, each holding a stolen brain. It thinks unlike any other creature. It speaks its own tongue and that of the diaboli, plus every language known to the brains it has swallowed.

Its bite deals 1d10 points of damage. Each stored brain holds one wizard spell of 3rd level or lower, castable once per day; roll 1d12 for how many it has, then pick or roll each spell (1d3 for level). Each round it either bites or casts one spell, and for all its alien mind it is a sharp tactician that uses its spells wisely. It fights carefully to avoid damaging its opponents' heads, since their brains are what it came for.

Though utterly alien, it is best called chaotic neutral. It means no malice; it simply does not see humanoids as people. Its true home is a far-off world, and it reaches the Prime Material only through tiny gateways near great magical power where space and time are twisted. It also appears on the Astral and Ethereal planes, and in the nightmare demiplane, where diaboli tell of it the way humans tell of dragons, as mighty, wily, and unknowable; its magic affects them. On the Prime it favors dark, quiet ruins and caves.

Arriving, it gathers brains as fast as it can, up to 12. It opens a slain victim's skull with surgical tools and swallows the brain, which settles into a pocket in its head. Once full, it hurries to return home, perhaps because 12 brains let it reopen the link in certain places; luckily such full collectors are rare and more interested in leaving than fighting. It may be related to the feyr.

It wants no treasure. To it, Prime Material natives are cattle, objects for detached study and ruthless use. It is a supreme predator but has little effect on the local environment.