Here are some useful links to the resources produced by the Royal College of Psychiatrists about the CASC exam:

The Online CASC exam guide - https://rcpyschcandidatecasc.z33.web.core.windows.net/#/

How the CASC is scored - https://www.rcpsych.ac.uk/training/exams/preparing-for-exams/casc-guide-for-trainees

Format of the CASC, including links to the generic mark schemes - https://www.rcpsych.ac.uk/training/exams/preparing-for-exams