Pen is an object in Downward Fall.
The pen is an ordinary pen. It has a tan tip and the stick part is black.
It first appears in the Kitchen when turning around. Fetty can be seen drawing the Box'N'Key poster with a pen. When the screen is black for 2 seconds Fetty and the pen are gone.
The pen also appears in Toys Faculty on a desk. The remains of the pen on the desk are most likely events of Fetty leaving the pen there after the flashback.