Mandatory Reviewers for Crucible

Go to Administration > Groups and add one or more groups named 'mandatory-reviewers-<project id>', where <project-id> is your Crucible project key written in lower-case. Add users to these groups.

Create a code review and add reviewers to it. You can have both mandatory and non-mandatory reviewers. A code review cannot be closed until all mandatory reviewers click the 'Complete' action.