The Bone Demon was tasked by the Foot Mystics to retrieve the Shredder's armor in order to revive the one true Shredder. He was given an amulet by the Foot Mystics that rendered him invisible, so that he could follow the Ancient One and sneak into the Lap of the Gods unnoticed.
Unfortunately for him, Master Splinter and his four young Turtle children had arrived to visit the Ancient One, in order to return Hamato Yoshi's ashes to his ancestral home. The Turtles were able to able to see the Bone Demon and were severely frightened by its presence, but their warnings were dismissed by Splinter and the Ancient One as the overexcited imaginations of young children.
The Bone Demon successfully followed the Ancient One to the Lap of the Gods, where he was able to reach the chamber where the relics of the Shredder were kept. However, he had been followed by Splinter, the Ancient One and the Turtles, and he attacked the old man and mutant rat, intending to kill them both. However, the Turtles overcame their terror and began flinging rocks at the demon, until Donatello succeeded in smashing the invisibility amulet. With their foe now visible, Splinter and the Ancient One defeated and killed the Bone Demon.