How I Stopped Worrying and Learned to Love Eberron
In nature, creatures who benefit each other in close proximity are said to have a symbiotic relationship. Small fish who clean sharks by feeding on their parasites, or crows that alert wolves to prey and scavenge afterwards. But the symbiotes found within the Realm Below are of a different nature.
The daelkyr of Xoriat are entities of madness, but think of themselves as artists. Their medium is living matter, and their works include such creatures as illithids, dolgrims, and beholders. They also craft smaller creatures, designed to physically interface with a creature and feed off of it while giving it a magical benefit. This could include: a tentacle that extends and acts as a whip in combat, an eyestalk that performs spells on command, a chitinous mass that acts as armor.
During the Xoriat Invasion, the daelkyr used these symbiotes as weapons and armor for their troops, but also as a way to infiltrate their enemies. After their defeat and retreat, many symbiotes were left behind and were able to survive and reproduce.
Recently, the dwarf of Clans Soldorak and Soranath have found caches and colonies of symbiotes and have begun to use them. Integrating a symbiote into a living creature is painful, and the symbiote feeds off of the person, but the benefits are significant.
But many researchers (especially among rival dwarven clans) say the risks are too high, especially if the symbiotes are able to communicate with the daelkyr. The exposure to symbiotes has even begun to change bloodlines; a set of children born in the Mror Holds have come out of the womb with a symbiote already attached, which cannot be removed without killing the host.