Guys this is the Rockwell from the recipes and explorer notes. He injected himself with molten element after experimenting with it, and it turned him into this. It killed Diana from the notes and left Mei Yin depressed.
This is the same person as Edmund Rockwell. He tested Element on many subjects ( that’s how Nameless and Reapers came ) and got greedy of their power and injected himself with it, turning him into the final boss. He destroyed the city’s ( how ruins came to be ) and Helena and Mei-Yin were forced to shove him into a hole and trap him. Helena, now depressed, held a funeral for Rockwell. That’s the story of how this horrid creature came to be.