The Bound are mated Blessed Shar.
Females are stark white and silent, and control groups of undead males, who are deep black and make a constant high pitched keening sound that disorients the living, causing hallucinations and euphoria.
Males are semi-incorporeal, fading in and out of materiality seemingly at random. At rest, they cling to the much larger females and feed off their blood, but they prefer the blood and flesh of the living, and bring the brains and organs to their female mates for them to feed.
Females are silent, but possess powerful magic. Males are bound to the female, and will vanish into nothingness if she dies.