I haven't actually read a fantasy novel with more than 10 million words, but I can provide you with some relevant information based on my knowledge of online literature. Fantasy novels usually involved magic, martial arts, myths and legends, and other elements. They often had rich plots and complicated relationships between characters. The inspiration for this type of novel came from ancient Chinese literature and Western fantasy literature. There were also many classic works such as Battle Through the Heavens, The Peak of Martial Arts, Douluo Continent, and so on. In the process of writing, fantasy novels usually focused on character creation and plot design. At the same time, they also needed a rich worldview setting and background description. In order to let the readers better immerse themselves in the story, the author also needed to use a large number of adjectives and epithets to create a unique atmosphere and artistic conception. Although 10 million words was a huge number, creating such a novel required a lot of time and energy, as well as constant exploration and experimentation. If you are interested in fantasy novels, you can read some classic works and draw inspiration and creative ideas from them.