The Book of the Magi is a special book where every single magical ability is written down in text. Everytime someone creates a spell this book writes another page by itself explaining this spell and how to use it. The book is currently in the possession of Magice.
The Mysterious Book of the Magi was never created by Magice but it was rather found by him floating in space. As Magice opened the book he saw the first page which was a list of it's owners, the book wrote down the name Magice by itself as he looked at the page. Magice was the second name in the list, the first one was crossed over and impossible to make out.