It is a black shoe that is sharpened to be a pencil.
Role in episode
When SpongeBob and Patrick get trapped in an alternate dimension, they realize they can make anything they draw come to life. When Patrick draws DoodleBob, they get their pencil taken away, and as a result, SpongeBob creates a shoe-pencil. He uses it to draw multiple allies and weapons to try to defeat DoodleBob. After multiple attempts, they finally defeat DoodleBob. When they draw Doodle Sandy, she draws a Doodle Vortex to bring SpongeBob and Patrick home.