Basically how it works is if you use the lights to rapidly switch between the light used to blind the guy and the stage spotlight, it can cause dialogue to not play. If you cause the fabricator’s dialogue related to the curtain being up to skip with this technique, the mask will come down early. You can also skip other pieces of dialogue but I’m not sure yet which other dialogue causes something to happen early from being skipped.

It’s often finicky about whether it will skip or not, but one thing to note is that it will only work if the curtain is fully raised to the maximum.