Deadly Smog

At rest, a deadly smog looks like any ordinary patch of low-lying fog, off-white and faintly musky, covering about a 10-by-10-foot area. In truth it is a misty core from which as many as fifty feeding tendrils reach out 15 feet. Its color never changes, even after a meal.

When it attacks, the smog convulses into a writhing tangle of tentacles reaching for every warm-blooded creature within 15 feet. A creature touched by one or more tentacles takes a single 1d6 damage in total. The smog drifts at movement rate 10 to keep as many victims in reach as possible.

For every 6 points it drains, it heals 1 point of its own damage. Once at full health, the extra points permanently raise its maximum, and each 8 hit points gained beyond its original maximum add a Hit Die without improving its THAC0.

Normal weapons pass through it harmlessly, and magical ones deal only their enchantment bonus, with no Strength bonus. A warrior of 18/00 Strength swinging a bastard sword +3 inflicts just 3 points, not the usual 10-17. Its weakness is water-element magic, which treats it as a natural weather effect: a cone of cold, for example, freezes it solid, leaving it open to being splintered, shattered and scattered, and while frozen it takes normal damage from all weapons.

Deadly smogs come from the Negative Material Plane, where they are uncommon, and never cross over willingly. Every one found on the Prime Material Plane, where they are very rare, was summoned, whether by accident or on purpose. On the Prime they always appear alone. How they reproduce is unknown, and probably best left that way.