While the flavor text of "Zure, Knight of Dark World" hints that the "Dark World" monsters are not intended to be evil, "Brron" may be the exception due to his psychotic nature (as a "Mad King"). This is supported by his role in the Anime as an antagonist.
Despite the Anime's portrayal of him as the single ruler of the Dark World, Master Guide 2 indicates "Brron" as subordinate to "Goldd" and "Sillva," who in turn report to "Reign-Beaux." (Who himself probably serves under "Grapha", and "Latinum" going by their Japanese titles)
This is supported by the colors of the monsters' names: Bronze (Brron) < Silver (Sillva) < Gold (Goldd) < Platinum (Latinum) < All colours/Rainbow (Reign-Beaux) < Black/Grey (Grapha)
Brron's hands appear skeletal at first, but at close inspection seem more like mechanical with pieces of flesh.