Header Editor

Each room in the game has a header with a lot of important information for loading the room. The first section of this editor is for background-related data, which affects the appearance of the room. Transparency, BG3 scroll, and effect are explained in the technical document. For transparency, it's easiest to find an existing room with the type of transparency you want and simply use the same value.
In MAGE Themes you can click on the notes icon next to the BG3 scroll input to open a list of all BG3 scrolls to quickly choose one.

This section also contains pointers and property values for the backgrounds and clipdata. The property values are explained in the technical document. Editing the pointers manually is not recommended unless you are working with a hex editor. MAGE automatically repoints background data for you.

The second section is for spriteset-related data. The pointers point to data which defines the position and properties of the enemies/sprites in the room. The set is which spriteset to use, and the event determines when to use the first or second extra set. For example, if the event for the first extra set is 0x47, then that set will be used if the event variable is 0x47 or higher. For Zero Mission, an event value of 2 is used for hard mode, and a value of 1 is used for easy mode. There should be no need to change the pointers, since MAGE handles this automatically.

The last section is for miscellaneous values. Map X and Map Y are the minimap coordinates for the top-left corner of the room. In MAGE Themes you can click the "Open Map" button, which opens a preview of the map and allows you to directly select the location of the room. The room bounds are displayed by a red rectangle.
Music is the default music track that plays for the room.