Stylus

From Zelda Wiki.org

The stylus is a pen-like object for use with the Nintendo DS and its touch screen.

In games most known as Touch Generation Games, you can play most, if not all, of the game without using any of the system's buttons, but just using the stylus.

Phantom Hourglass Stylus

During the beginning parts of Phantom Hourglass's release, Nintendo of America ran a promotion in which, after registering the game on their Web site and taking the subsequent survey, they would send the person a Phantom Hourglass-themed stylus which was clear and shaped like a feather pen.