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A Key Mind is an exceptionally advanced form of the Flood. Several were formulated during the Forerunner-Flood war to combat the Forerunners with pure strategic might. The use of Precursor technology gave each Key Mind incredible processing power and strategic skill that easily matched that of a Metarch-level Ancilla, such as Mendicant Bias or Offensive Bias. Being a compound, distributed intelligence, each Key Mind was an extremely large and well-developed instance of the Gravemind entity. These enormous collective consciousness composed the leadership of the Flood, coordinating their efforts throughout their war with the Forerunners. Each new instance added to the overall Gravemind's intelligence and computational power.