Empress Defeated (in kMST)

There's no such thing as a "mirror of the real server" unless you're implying Nexon's server sources have been leaked (recently).

Everything that is server side, including drop, boss behavior, "anti-hack" measures such as hidden drop conditions or map kickout, death notices, death buffs, and so on, is rewritten in the private servers.

There have been no server source leaks of gMS. The only code that's been "leaked" was that code that kMS accidentally put in the .wz files in a kMS(T?) patch a little while ago.

Basically this. Private servers are only made to look like they mirror the real server. It isn't very difficult if you've got someone who's good at Java. There isn't very much that can't be altered, added, or removed as far as private servers go. Last I knew of the only real thing that couldn't be was added/removed was jobs/skills.