Completing an achievement earns you an achievement point. These points add to your ranking meter in the plot. The higher your ranking, the higher your final trophy level will be. So try to complete as many achievements as you can!
What are Achievements in The Wraith Resurgence?
Achievements are special bonuses that you earn in the plot. These bonuses can either be prizes, an increment to your achievement points or both. Achievements are available for each activity in the plot. New achievements will be added as the event progresses, so keep checking back to see what's currently available for you to attempt.
looks like there might not be a final prize shop based off of this information