The net code for a bullet hell multiplayer shooter is... not simple, mildly put.
There is a snippet of how they handled it in this article... http://t-machine.org/index.php/2012/03/ ... etization/
It is definitely not a common authoritative server with lag compensation set up. I found that to be mostly unworkable in a high precision environment like ROTMG when I tried to make a clone - it takes too long for the host to create/update/destroy objects and relay them back to the peer.
There are definitely workarounds, such as those the ROTMG team took, but you have limited control over packet interpolation/extrapolation in the multiplayer plugin.