The darkness elemental is also very similar to the shadow elemental from the 3e Tome of Magic, which includes several similar abilties and bits of lore.
Darkness elementals attack creatures with an incorporeal touch that ignores armor and blinds those who are hit by it (the blindness is removed in any bright light). They suffer damage from light-based and healing magic, which also causes it to explode violently outward, damaging nearby creatures. Darkness elementals can also hide in shadows, as long as they are immobile.
Darkness elementals are not very well known, though it is hypothesized that they have caliphates or sultanates with a more-or-less fuedal structure on their home plane, in mirroring other elementals. It is possible, though, that given their evil nature, they have organized under a prince of elemental evil, or a yugoloth lord of some sort.
The elementals have been found in the company of dao, and undead creatures tend to travel in their groups.
- Dragon Magazine #227 (2e)