Appeal can be compared to what be charisma of a real life actor. People often narrow appeal into the category of cute characters, their appeal of the viewer wanted to cuddle them, but monsters and such can have appeal too. The main concept is that they are believable, real and interesting. Appeal relies on the features of the character, the design. If you wanted the characters appeal to be cute the design could have baby- like features and symmetrical face. An animator would not design a cute character with small, unsymmetrical eyes or a sharp long nose as the appeal for the character type would not be believable.
Appeal lends itself with design. A character can have the desired appeal as long as the design is right.
This example is perfect for showing appeal with the design of the witch and Snow White. They are excellent contrast to show both negative and positive appeal.