Bonefarious believed Skull's eye color would be a bad omen, and referred to him as a "vile beast". Ironically, Bonefarious' own name is a portmanteau of "bone" and "nefarious", which means "vile".
Before the journey
Bonefarious first appeared in a flashback memory Skull had during chapter 7. Due to his belief that Skull's blue eye color would bring deadly tragedy, he attempted to kill the young Marowak after he was just born. A Marowak named Guardia protected Skull long enough for Bonefarious to be banished by the Marowak tribe leader, the Skulled Head.
The unwilling reunion
As no one knew of Sinnoh at the time Bonefarious was banished, it was considered "uncharted territory". While there, Skull encountered his father and battled him one last time. Eventually, Bonefarious was killed when he landed on a rock after falling from a tree.
Like Skull, Bonefarious is severly effected against Ice-, Grass-, and Water-type attacks, though he is also weak to Skull's Shadow attacks. He has learned Focus Blast during his time in Sinnoh, and it was revealed that Skull had inherited Swords Dance and Rock Slide from him. Bone Club, Bonefarious' final attack, was used somewhat commonly throughout the fight.
Bonefarious is consistent in his belief that Skull would bring horror to the world, and believes him to be an abomination. He also seems to dislike being called the real abomination, as proven during the flashback memory. Bonefarious is just as his name suggests: a vile Marowak with a hatred of his son, ironically believing Skull to be vile.