Well, there was numerous debates about whether this was wrong or right. Although I believe that many times, the authorities mentioned that dual clienting [on the same comp] isn't an offense at all. All I can say is it's useful when you need to trade between characters and you won't fear getting cheated if there's no one trustworthy online. Only need it if you have a computer though.
I'm going to make this thread just for reference though, you can easily google "dual client flyff" and find it on the net.
1. Go into your C:..Gpotato/Flyff and you will find two .exe files named Flyff and Neuz.
2. Make a SHORTCUT [not copy/paste] out of Neuz onto your desktop.
3. Locate your shortcut of Neuz and go into properties/shortcut/target
where you will see "C:Program FilesGpotatoFlyffNeuz.exe"
4. Add sunkist to the end of the target so it becomes "C:Program FilesGpotatoFlyffNeuz.exe" sunkist
5. You should make your flyff client into window mode/800*600 so you can dual client.
6. Double click on flyff and let it run the patch
7. Click on start when patch is done. Watch for gameguard to finish initiating.
8. This is a moment of timing. Double click on the Neuz shortcut as soon as the gameguard is done.
9. And just wait to see if you have two clients ready to be played with. If not, it would be written "Hack is found", but I can assure you it's only because gameguard sees itself as a denied material which results in the message. Just trial and error till you get the hang of it.
Notes: I wouldn't recommend you to tell anyone you are dual clienting on a single comp though, they might always suddenly find it illegal and bad things happen. If you don't talk about it, there is no way they can find out if you are playing on a single computer or two computers.
Knowing more is better than knowing less, so I would call this thread a reference. Until proven guilty, the accused is always innocent. Remember that, and speakth not the wrong things to the wrong people and you will never be in the wrong. :p