Nishruu

A nishruu is a soundless cloud of red, breathable vapor with no organs or features. It glows and pulses steadily as it drifts and can seep through cracks a finger wide. Old sages named them eaters of magic, and they probably hail from some other Prime world.

A nishruu does no harm to bodies or objects; all its damage is to magic. Within 60 feet it always flows toward the densest concentration of magic, heedless of attacks. Mundane blows and nonmagical flame harm it normally, and a foe inside its cloud cannot miss. Magical cold and fire launched from outside deal half damage and are absorbed after one round, and such effects cannot be created inside it. Illusions and mind control fail. Any other spell cast at it is simply eaten, granting it hit points equal to the damage the spell would cause, or equal to the spell level for spells that cause none.

Touching it costs a charged item 1d4 charges, and again every other round if the touch continues. Other magic items go dead for 1d4 rounds after contact; potions and scrolls used during contact take effect only 1d4 rounds after it ends. Artifacts stop working during contact and for one round afterward.

An engulfed spellcaster of any class loses one random memorized spell on contact and another each round after. With each loss the caster must save vs. breath weapon or suffer the effects of feeblemind for 1d4 rounds.

Nishruu are solitary outsiders that cannot hand off absorbed spells or charges. Sea salt and rock salt alike are deadly to them; a thrown handful usually inflicts 2d10, and because they shun it, lines of salt can corral or steer them.

A nishruu senses magic up to about 600 feet away and wanders after whatever is nearest, richest or strongest. No limit to what it can absorb is known, and none has ever been seen to starve; sages think sunlight and moisture may also feed it.

When slain, it fades, loses its color and seems to sink into the earth. Every magic item within its body at that moment, and any magic weapon that dealt the killing blow wherever it is, gains 1d6 extra charges, or one extra use if it is a single-use item like a scroll or arrow. Uncharged items, artifacts, potions and memorized spells get no benefit.