Here's how to multi-client Dragon Nest Europe (version published by Shanda Games or Steam). It's pretty easy. Still works as of today, 22-FEB-2015.
Please note that DN EU has almost 0 protection, so this method may not work on other versions.
0. Sandboxie is required for this, so download and install it. Official site:
http://www.sandboxie.com
1. Go to your game installation folder. For Windows 7 the default is:
C:\Program Files (x86)\SDGi Europe\Dragon Nest Europe
2. Open Notepad, paste the following command line, and save as ANYTHING.BAT
DragonNest /ip:211.43.158.237;211.43.158.238 /port:14300;14300 /Lver:2 /use_packing /language:ENG
3. Right click on ANYTHING.BAT and select Run Sandboxed
After these steps, you are free to open another DN instance normally through the regular dnlauncher.exe