The main purpose of this website is to teach you XML for Realm of the Mad God.
However, a great Boss or Monster is not only made of code: it also requires a good and detailed design idea!
Before you jump into scripting, you should think about it and lay down the concept of the Monster you want to create. This will help you break down the work into pieces such as phases, transitions, attacks, movement, difficulty and feeling for the Monster and get a better overview of how you should structure your code.
Check out this complete Dungeon Template to create great concepts! (Credits: Sues)
Is something described here not clear or do you have ideas on how to improve the documentation? Let us know!