Pen is a robotic penguin enemy found in Sonic Advance's Ice Mountain Zone. They walk back and forth, and when approached, they make a stop and launch snow balls at the player. Just jump over the snowball and hit the badnik, and you'll be fine. Pen's appearance highly resembles Penguinator of Sonic 3, but their methods of attack differ.
A newer model of Pen reappears in Sonic Advance 2's Ice Paradise Zone and behaves similarly to Sonic 3's Penguinator badnik in the sense that rather than launching a projectile it will instead charge at the player. Unlike Penguinator however, this version of Pen does not stand up at any point, and more resembles a penguin'esque missile.