From the Super Mario Wiki
Dark Boomboxers are pitch black, shady counterparts of Boomboxers found in the game Super Paper Mario. They are found in rooms 34, 36 and 43 of the Flopside Pit of 100 Trials. These strange creatures have a radio-shaped head, and spend most of their time playing loud music and listening to it. When they spot an intruder, Dark Boomboxers attack by emitting loud sound waves. Unlike regular Boomboxers, Dark Boomboxers shoot six sound waves at once. Like their weaker relatives, Dark Boomboxers have high HP, and cannot stand explosions: indeed, detonating Boomer temporarily stuns all Dark Boomboxers on screen.
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