User blog comment:DarkAngel Reid/Doboruberuku/@comment-2097722-20101118140639/@comment-87.217.45.240-20101118141454

They wouldn't reveal the offline boss before releasing the game.

And besides, I think the boss would have a specially designed map for fighting it (such as the Battleground for Akantor or the Snowy Peaks for Ukanlos), and this guy seems to be in the standard Mountain Stream. So I doubt it.