Intermediate Developer Examination is basically to gain the advanced knowledge of various topics that you may have already done in your Rapid Development Course (For example – Advance Domain Model, Better implementation of Microflows , Advance Page building , Details of REST Integration etc.) , and some new topics like UX UI and Front End, Styling App with Sass , Workflows.
However, the Rapid is for the basic knowledge you need to build an app, where as Intermediate course will help you with a better understanding of what actually you are doing in your app with some amazing features and functionalities.
So, go ahead and start the journey of becoming Mendix Intermediate developer.