This is not optimus's fault, it is Mabinogi's crappy ass client.
Below are images of what mine looks like for my laptop that uses optimus.
[Image: http://puu.sh/5YcN1.png]
Under 2. on the image, you can switch it to auto-select or force it to use one of the two cards.
For turning on the little icon, under the nvidia control panel click the desktop drop down menu at the top and make sure "Display GPU Activity Icon in Notification area" is selected. Now, you should have an icon in your display area in the bottom corner of your screen that looks like this:
[Image: http://puu.sh/5YcXd.png]
. When you run a program that uses the nvidia card, the icon will change to look like this:
[Image: http://puu.sh/5Yd7Z.png]
Hopefully that is some kind of help. I noticed some people were mentioning it and not working, but mine works just fine. I wasn't sure if you did these steps or knew about it, so just trying to offer some insight! :)