Brug Mass has appeared once so far in the series.
 Metroid: Other M
The Emperor Brug bonds with the swarm of Brugs to form the Brug Mass after Lyle Smithsonian kills a Brug. After it is sufficiently weakened by the efforts of Samus Aran and Platoon 07, the Emperor Brug pops out and is destroyed, and the Brugs disperse and scurry away.
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