Write the brief, not the picture

I want an image of: [ROUGH IDEA]

Do not generate anything yet. First write me the brief, separated into:

1. SUBJECT — what is literally in the frame, and where.
2. TREATMENT — medium, lens or brush, light, palette, era.
3. MOOD — in three words, no more.
4. WHAT MUST NOT BE IN IT.

Then give me the prompt as one paragraph, subject first, treatment second, with no adjective doing two jobs.

Then tell me the one thing about this brief most likely to come out wrong, and the phrase to change if it does.