Egarus

The quasiplane of Vacuum is an endless, mind-numbing nothing, one of the emptiest and loneliest places in the multiverse; by comparison even the Astral or the deepest layer of the plane of howling winds feel crowded. That is exactly why the canny use it as a dumping ground for things that must vanish from existence for good. The egarus proves that this does not always work.

The story begins with a fool who visited a supposedly 'safe' layer of the Abyss and came home to his prime world with a scrap of fungus stuck to the toe of his boot. In that unguarded world it grew explosively. He threw the boot away, but the growth swallowed his house, then his neighbors', and fire would not touch it. Within days it covered half the town, which named it egarus (the word is said to be a curse). Wizards' spells and devices killed some patches, but the wind had already scattered spores across the region, and patches thought destroyed kept springing up elsewhere.

At last several gods with large followings on that world answered their worshipers' pleas and opened gates to Vacuum. Over many generations the mortals gathered every scrap of fungus, using newly devised detection spells to be sure none remained, and pushed it all through before the gates were sealed. With nothing to eat, it was sure to die.

It did not. It learned to feed on absence itself, thriving on the lack of matter and energy, and now drifts through the void in tiny dull-white clumps, sucking at the nothing like a leech. They do nothing to draw attention, and a traveler on the plane would be very unlikely to find one even while searching. Yet they are a grave danger to anyone foolish enough to go there.

Substance of any kind, other than itself, is intolerable to the egarus. A patch can sense matter thousands of miles away, though distance means little on Vacuum, and it closes the gap with a power much like teleport without error (it cannot use this to leave the plane). Once within 25 feet, it begins slowly disintegrating whatever it found. No magical protection or magic resistance helps, since protections are broken down too.

Energy goes first: light sources, flames such as torches or burning magic weapons, and active spells, one per round per patch in random order. Then it unmakes nonliving objects one at a time until nothing stands between it and the living. Magical items and creatures may save vs. disintegration or death magic to resist.

Destroying a patch is the only way to stop it, and luckily that is not difficult. Shocking grasp, lightning bolt, disintegrate, finger of death, slay living or cure disease kill a patch instantly, as does any acid, alcohol or electrical attack, or a flood of at least 60 gallons of water to dilute and scatter it before the plane's cold freezes the water solid. Hold monster, hold plant or slow halts its attacks. It is immune to fire, cold, physical blows and other spells.

The egarus has settled comfortably into its exile and attacks every visitor, since intruders threaten the emptiness it needs.

It presumably spreads like other fungi once it has fed, and no one can say how many clumps now float in the void. Ironically, a patch carried off Vacuum, say on another unlucky boot, would starve, since it now needs emptiness to live. Before dying, though, it would destroy huge amounts of matter trying to carve out a void to survive in.