Stats: Elder Brain
The Nexus Encephalon was the Hive Mind which hosted the consciousness of the colony of Mind Flayers known as the Unknown. Dismalaravas and Zeph'yrgai'arux are such members of this colony and hive mind.
The tendrils of this elder brain colony stretched across the Planes: Al'tehrun, Umbradeep, Chimerazon, Void, and Seraphar were the discovered Planes with Nexus Encephalon presence.