Which characteristic is typically associated with the 'evil twin' trope?

The 'evil twin' trope is characterized by a twin who embodies traits that are in stark contrast to those of the protagonist. This stark difference often highlights moral or ethical dilemmas, as the evil twin typically represents negative qualities such as deception, selfishness, or malevolence. These contrasting traits serve to enhance the protagonist's virtues, making the conflict between the two more pronounced and engaging for the audience.

While aspects like assistance or heroism may be present in some narratives, they do not align with the essential nature of the 'evil twin' trope, which is fundamentally about opposition and conflict between the twins' characteristics. The idea of a mirror image captures similarities rather than the distinct contrasts that define this trope.