The Phantom of the Opera is where Gibson, Walter B. got the idea for the Secret Sanctum, because the Phantom's underground dwelling, under the opera house/theater was called his sanctum.
But what about the power to cloud men's minds? Oh sure we see it today in "the Force can have an effect on the weak minded" bit from Star Wars, but where did it come from?
Not to be a know-it-all, Greggie, but the "red scarf-like mask" had nothing to do with the Scarlet Pimpernel, as SP wore disguises, not masks. The red was added for the sake of adding color and contrast to the magazine covers.
The Scarlet Pimpernel was a master of disguise, as were the Shadow and Batman. Pimpernel was the influence for the modern superhero in that he had a dual-identity; a aristocratic fop to the public but a heroic swashbuckler in his heroic persona. This was a direct influence on Johnston McCulley in his creation of Zorro. Of course, the film image of Zorro in "The Mark of Zorro" with his wide brimmed had and all black outfit is a visual influence on the Shadow.