Nelyth is a planet that is/was held by Daelaam forces. It held spiritual significance to the protoss, and prayer tiles were set up through the settlement's streets.
During the Second Great War, Abathur became aware of the mitoscarab, a creature native to Nelyth that held useful essence for the Swarm. Its essence was assimilated, allowing banelings to morph into splitters. The new variant strain ran rampant, eradicating the protoss forces stationed at a nearby shrine.