Complex sentence: He was banished for his belief that diseases were caused, not by evil spirits, but by viruses and bacteria, only to return to treat Glacian, the genius of Halcyon, who was stabbed with an imperfect powerstone by an Untouchable named Gix.
Split into simpler sentences: He was banished for his belief that diseases were caused, not by evil spirits, but by viruses and bacteria. He later returned to treat Glacian, the genius of Halcyon, who was stabbed with an imperfect powerstone by an Untouchable named Gix.