Ouyang Feng
Ouyang Feng forces Guo Jing to produce a copy of the manual for him in his bid to become the most powerful fighter in the jianghu. Guo writes a fake copy of the book, with some changes to the text that only a really seasoned martial artist can detect. Some numbers were changed and verses were written in reverse order.
When Huang Rong is taken hostage by Ouyang Feng later, he forces her to translate the last few verses in his copy obtained from Guo. Huang subtly changes the translated text and causes further complications. The result of all those "edits", ironically, increases Ouyang's powers but also causes him to become insane.
Read more about this topic: Jiuyin Zhenjing