Vacuous

For all the tidy theories of a law-obsessed faction of sages, the Inner Planes leak. Negative energy seeps elsewhere and drags wraiths, spectres and other spirits with it. Most are hauled back home, but a few slip away. The vacuous is one that drifted onto the quasiplane of Vacuum and escaped recall by losing itself in that boundless nothing. The void remade it as a short, big-headed humanoid with beady black eyes and eggshell-white skin webbed with fine cracks. Stubby arms end in long black claws, but what draws the eye is its enormous mouth, inside which there is simply nothing: it holds its plane's emptiness within itself.

Two claws rake for 1d6 each. Worse, it can open the void inside it and aim its mouth to draw in one target within 25 feet. The victim must brace and pass a Strength check at -2 or be hauled close, where both claws hit him automatically that round. After one round of pull, the vacuous must end it, switch targets or swallow the victim whole. A full belly leaves it unable to move or attack, so it usually waits until other foes are down, though in a pack some may swallow while others guard. A victim pulled to the lips makes a second Strength check at -4: success means clinging to the outside, helpless and taking two automatic claw hits, while failure means being sucked into the hollow body, pinned in place, to die of suffocation and heat loss in 2d4 rounds unless the vacuous is slain. Priests turn it as a wight. It is immune to poison, paralyzation, cold, negative energy and mind-affecting magic such as charm, hold and sleep.

These cunning undead hunt in packs. They may drive prey toward hidden packmates, spread out to strike from several sides and pull a group apart, or take turns yanking a lone foe back and forth so he can never recover. Ambushes are hard to set in a featureless void, and their home offers food only when rare visitors arrive, so they gladly travel through summonings or stray gates to planes richer in prey.

A vacuous will eat any living thing, body and brain, leaving nothing. Its own form is hardly physical, a shell of planar energy drawn from Vacuum and the Negative Energy Plane, which means it is made at least partly of nothing.