First published in 1972, Walt Lee's REFERENCE GUIDE TO FANTASTIC FILMS was an early work that attempted to capture the imagi-movie ouevre in an encyclopedic form. Along the way, he contributed a series of articles for FAMOUS MONSTERS that focused on the elusive mexican monster movies.
Cited as the first mexican horror movie was 1934's PHANTOM OF THE CONVENT. The next wave came in 1952 with THE RESURRECTED MONSTER, followed by THE BODY SNATCHERS in 1956, then the German Robles series of vampire films that we are most familiar with.
You may remember the image from THE BODY SNATCHERS from my post, What Scared Me. Pictures such as this promised unrequited desires. It wasn't until exploitationer K. Gordon Murray imported a number of horror films from south of the border that we got our wish. Dubbed and retitled with English variations we finally saw what had been thrilling audiences in Mexico. My clearest recollection was watching THE WITCH'S MIRROR on a rainy weekend. The atmospheric film gave this young Monster Kid a bona fide case of the creeps!
It is mentioned in this article that masks of the Universal monsters were frequently used. Lee mentions that the Don Post masks were used "with various additions to complete the costume."
Here is the first part of the series, published in FAMOUS MONSTERS OF FILMLAND #121 (December, 1975).