Tribe of Darkness
The Tribe of Darkness is a group of powerful beings who broke off from the rest of the Tribe of Ancients 2,000 years before the events of Super Paper Mario. The tribe is known for being a secretive bunch that kept to themselves and forbade marriage outside the clan for fear of diluting their powers. They were also accused of stealing the prophetic Dark Prognosticus from the Ancients, with some suspecting they intended to use the book to enhance their dark magic; however other stories explain that they did it to prevent the book's power from being misused. Nolrem is a descendent of the tribe, and Count Bleck is the last surviving member of the tribe itself, having destroyed the rest of the tribe after his father seemingly killed the girl he had fallen in love with. In addition, it is hinted that Nastasia was originally a bat that was transformed into a member of the same species as Bleck, whom she had fallen for, which would make her a member of the Tribe of Darkness as well.
Three thousand years before the events of Super Paper Mario, an Ancient magician used knowledge gleaned from the Dark Prognosticus to create "thinking tools" known as Pixls to work around his people's physical limitations. This allowed the Ancients to build a vast civilization, however a thousand years after the Pixls were created, a huge Pixl appeared and used her powers of mind control to turn the rest of the Pixls against the Ancients, devastating them and sparking the decline of their civilization. A group of warriors, assisted by the other 12 original Pixls, defeated the so-called "Pixl Queen", and the single surviving Ancient warrior discovered that she had actually been the first Pixl created. In order to prevent the knowledge contained within the Dark Prognosticus from being misused like that again, and potentially causing more tragedies, the Ancient warrior took the book and went into hiding, eventually founding the Tribe of Darkness.
Despite their altruistic origins, the secretive nature of the Tribe of Darkness soon earned them mistrust, with some accusing them of stealing the Dark Prognosticus to use it, rather than hide it. Despite this accusations, the Ancients recognized that the power wielded by the Tribe of Darkness was an important resource, and called upon the tribe when they built Flipside. Alone, Flipside was unstable, for light cannot exist without darkness, and so the Tribe of Darkness created Flopside, a dark, mirror image of Flipside, thus stabilize the realm. Nolrem, a descendent of the Tribe of Darkness, could still be found residing in Flopside centuries after its creation, during the events of Super Paper Mario.
Some time after this point, the Tribe disappeared from the Ancient's watch entirely, instead going to live in a castle in a forest, far from any outside contact. Their xenophobia is said to be based on pride at one point by Carson, although they were also concerned that their magic would become diluted if they married outside of the tribe. However, this line of thought eventually led to their downfall, as shortly before the events of Super Paper Mario, one of their own, Count Bleck (then known as Lord Blumiere) fell in love a human descendent of the Ancients. Then, when his disapproving father banished the girl from their world, Bleck opened the Dark Prognosticus and used its power to destroy the rest of the Tribe of Darkness and spark the events of Super Paper Mario.