Though somewhat misidentified (i.e., there is no black pit), The Black Pit of Dr. M (aka Misterios de Ultratumba) nonetheless delivers the goods in a fashion that only a Mexican gothic horror film set in a sanitarium could—with disorder, murder, acid-throwing, and a ghost MD controlling everything from beyond the grave. The release is part of Casa Negra Entertainment's great series of remastered Mexican horror classics.
The orchestral score for Dr. M is also noticeably above average. Here are the main titles, music by Gustavo C. Carrion (yes, Carrion! -Ed.):
>>>The Black Pit of Dr. M - Main Titles