- “Why does everyone feel so happy when I leave?”
- ―The final quote of Bart's guilt.
After Bart threw away Lisa's hat, he felt guilt for the first time and was visited by a humanized version of his guilt, which grew as he felt more guilt. When Lisa forgave Bart, his guilt shrunk, got knocked out by an airplane, and landed in the Springfield Nuclear Power Plant, where it mutated into a giant monster, much to the enjoyment of Mr. Burns.
Bart's guilt looks exactly like Bart, only it's colors are a bit more darkened and dreary looking. The spikes of his hair are more messy and they wilt over a bit. He also has more elongated fingers and his shirt is more sloppily tucked in. He has dark black bags under his eyes and a lot more of a grindy and raspy voice. The more Bart's guilt grows, the more green his skin will become and the more his clothes will rip apart. It also has much longer arms than Bart.
Bart's Guilt is a pestering, manipulative demon, who stalks Bart at all times, constantly reminding him of his wrongdoings, and making him feel more and more guilty about it. His haunting of Bart, gives him full control over his emotions, by making Bart think whatever he wants him to think. The only way to get rid of him is for Bart to overcome his guilt, which makes Bart's guilt feel very depressed and rejected.
- One of his forms resembles Hugo Simpson II.