Elder brain

The Elderbrain is the collective minds of past Illithid that resides usually in the center of an Illithid hive. It psychically connects all Illithid to each other and provides knowledge of past events, anything that an individual Illithid sees, and is considered sacred by the species.

K'Varn gained control of an entire city of Illithid by erecting a crystal like structure above the Elderbrain which allowed K'Varn to control it. Later, Vox Machina nearly destroyed the Elderbrain in an attempt to escape from the Mind Flayers within the city.