This demon is not a separate entity but rather a manifestation of the characters' own struggles with addiction. The characters are pulled toward their vices by their internal demons, represented by this shadowy figure.
The demon's appearance changes depending on the character's addiction and desires. For example, Sally's addiction demon is a horrifying, bloody figure, representing the blood she lost due to addiction. Liz Taylor's demon is a more elegant and glamorous figure, reflecting her addiction to fame and attention.
The demon is a powerful symbol of the destructive nature of addiction and how it can consume a person's life. It also highlights the power of temptation and how it can be hard to resist, even when you know it's harmful.