Filter merge requests by participant
In the "Merge Requests" panel, you can filter with "Assigned to me", "Created by me" and "Everyone's". There should be a "Participating" filter, that shows all merge requests on which you are a participant.
This would be useful when you are added to a merge request as a participant (ex: "@You" in the comments). You receive an e-mail and appear in the list of participants, but there is no way to find those merge requests except by looking through your e-mails. Also, the API doesn't have the "participants" field.