Upon being marked by a shadow creature with a hunger for humans, a duplicitous man is exiled from his hometown and forced to confront his identity or face losing himself.

The goal for a protagonist should be to restore the balance offset by the inciting incident. What does confronting himself have to do with the monster? Losing himself... literally or mentally? This still has nothing to do with the monster though. If he's earmarked for death in the inciting incident the goal should be to become un-earmarked by killing the monster or simply surviving.

What does his duplicity have to do with anything? Usually the characteristic helps to suggest an arc for a character or can be used to suggest a method in which the hero will carry out his task. In this current logline I don't understand what bearing that has on the story.

Why is he exiled?

As others have pointed out, this is all a bit confusing and disconnected. There needs to be coherence with all the elements for the story to work.

The logline is confusing - the parts aren't adding up.

What is his goal by the end of the story?

In what way is being marked a bad thing for him? Is his life in danger or are the people around him in danger now that he's marked?

How does the shadow creature and being exiled connect?

The disconnect between the two things is making the logline Jarring.

He is targeted by a shadow creature, so you would think the plot would be to destroy the creature, instead, he is targeted by the creature so he decides to go find himself.