Complex sentence: A devastating nuclear war, that the Justice Guild died in, had all but destroyed the world; the aftereffects of the nuclear war had granted him psychic powers, but mutated and deformed him into a hideous monster.
Split into simpler sentences: A devastating nuclear war, that the Justice Guild died in, had all but destroyed the world. The aftereffects of the nuclear war had granted him psychic powers, but mutated and deformed him into a hideous monster.