During Kirby's Reign, the Cannibal found a psychic Pokemon named Mewtwo. Kirby, knowing that he would not endure forever, decided to create a horrific legacy that would last long into the future by leaving the terror he caused behind. Kirby started this plan by seeking out Mewtwo, torturing him into madness, but leaving him alive.
Mewtwo eventually rose to power as the first of the dons in the Mushroom Kingdom besides Bowser. During the Reign of the Elite, the Pocket Monster planned to end the stalemate between the four dons and create a psychic army to take over the Mushroom Kingdom. He raised his army, consisting of immigrants and Pokemon, at an orphanage that he owned, experimenting on their DNA to give them their psychic power. He also trained them brutally and isolated them from the outside world. However, his army would not come to be. Rumors spread about the orphanage, and the immigrants and Pocket Monsters lived in fear. The fear they lived in combined with the misery Mewtwo inflicted upon them eventually drove them into madness. Some of them had to be executed, while others were institutionalized, possibly at Petal Meadows Asylum. However, Mewtwo managed to keep two children, Ness and Lucas. It was these children that would be his undoing.
The demons, in their vendetta against humanity, found the Shadow Don, Ganondorf Dragmire. Admiring his power, they led him to Ness and Lucas, who had gone completely insane from the misery they were forced to endure. Ganondorf saw potential in these children, planning to use them to annihalate the rest of the mob and take over the Mushroom Kingdom. He was able to sustain control over them with the Demons' help. He guided them, having them kill for practice, before turning them on their master, as by now they were regal enough to turn against the one who'd inflicted so much upon them. Ness and Lucas tore out Mewtwo's intestines and stuffed them into a Pokeball. However, it was at this point that Ganondorf realized that he had made the same mistake that Mewtwo did. He saw how they would kill anybody or anything to satisfy their own malice and self-hatred. What he saw destroyed most of his sanity, but he managed to keep a firm grip on reality.
Ganondorf later used Ness and Lucas to kill the other dons. Eventually though, when all of the other dons were eliminated, Ness and Lucas got out of control after the Demons were destroyed by Mario. Ganondorf, having had enough, planned to die along with the kingdom to escape the two insane children. During the Battle of the Ivory Towers, Kirby came, killed Ganondorf, and retrieved his progeny, being the only one who knew how to control Ness and Lucas. However, an explosion caused by Luigi in the towers stopped Kirby in his tracks. Kirby survived the explosion, but it is unknown what became of Ness and Lucas.