Final answer:
Mason is planning to attend a Dress Rehearsal, which is an essential part of the production process where all technical elements and costumes are included to mimic showtime conditions.
Step-by-step explanation:
Based on the context provided about rehearsals, technical elements, and the inclusion of costumes and lights, Mason is planning to attend a Dress Rehearsal. Dress Rehearsals are when the production is run under showtime conditions. This means that everything needed on opening night, such as sets, props, lights, and costumes, are utilized to ensure that the cast and crew are prepared for the audience. The actors practice with their costumes, execute their quick changes, and work through any potential issues. These rehearsals are critical for integrating all aspects of the production, from the designs brought in by creators to the stage manager's role in calling the show. It is an all-encompassing preview of what the audience will experience.