Write the actual prophecy as a 2-line verse. Then, burn it. Ask: What if the prophecy is wrong? Misinterpreted? Deliberately forged? Your entire script will be more interesting if the prophecy is unreliable.
The cave hums with a low, vibrating blue light. In the center, a rusted sword is wedged deep into a glowing white stone. The Chosen One Script
After analyzing over fifty produced screenplays (from The Princess Bride to The OA ), a clear seven-beat structure emerges. Use this as your template. Write the actual prophecy as a 2-line verse