With the mouse is a little box, that contains four weights. Each of these weights weighs 5 grams, and you can chose how many you want to use. In this way, you can optimize the weight after what you need, and feel is the best for you personally. The mouse itself weighs 126 grams - without the USB cable.
There is also an ID-card, as you normally find it with Roccat products. With the ID-card, you can register online at www.roccat.org.