It doesn't require much of an imagination to see that the hulking Massassi are genetic cousins to the Sith Pureblood. Both share the same distinctive skin tones, skeletal ridges and body tendrils. Both are also Force-sensitive, though the similarities typically end there. Nourished by the dark side of the Force, the yellow-eyed Massassi have developed a culture based around hunting, combat and violent ritual sacrifice.
On Yavin 4 in particular, the Massassi are markedly different from Purebloods. These impossibly strong warriors have developed dense and sharp claws on their hands and feet, and their intellect has diminished to the point that they rely almost entirely on animal instinct and use grunts to communicate. Their society, such as it is, has devolved into true barbarism.