The ghost is Malgrum’s past. He forgets his memories but only sees flashbacks, and his flashbacks show that he may have been a bad person. In the most frequent reality he is in, he is evil. He is set on destroying the entire reality, and all life in it, and Malgrum is appalled that he did that. However, he doesn’t have enough information to see the full perspective, so he doesn’t get the full view.
Before that happened, he lived in a reality of celestials, which was balanced by two orbs, the orb of light and the orb of darkness. A selfish celestial wanted the power to create a reality of his own, so he took the orb of light, since it was the easiest to control, and used it to leave the reality. Because he took the orb, the reality they were in began to collapse, and Malgrum, who was losing his home, friends, family, and love interest, decided to take the orb of darkness, which is almost impossible to control, and used it to follow the being who took it. When he arrived in the reality, time had gone by differently, and there was a whole civilization over a giant planet. Malgrum was able to create a moon of the planet into his home, where he started to create an army to destroy the life in that reality. He did this for many reasons, as he was firstly consumed with rage to begin with, as he lost everything, but the orb of darkness also entails rage, so Malgrum had to learn to control the orb to control the over the top rage. The main reason, however, was if Malgrum obtained the orb of light, then he had the ability to restore his reality, and then hopefully find the people he had lost.