Values are used to create the effects of light and shadow in a drawing. To make your drawings look realistic, you will need to replicate these different light effects.
A Natural Light Source
Moving the light source from below the subject to above gives the monster a less frightening appearance.
An Unnatural Light Source
It’s more than just a bad haircut that made Frankenstein’s monster look scary. Placing the light source below the subject contributes to his frightening looks.