Guild Wars 2

http://www.gw2db.com/achievements/359-king-of-the-costume-brawl

Does anyone know what is the reward for defeat 500 people? Maybe a title, or something completely different?

No i believe there is no title given, else there would be a Crown on the right hand side of the progress bar. It would be too exploitable for a title for two friends could afk while another whacks them to coninuously become champion hundreds of times