Nightmare In Blood was filmed in 1973.
The theater in Oakland, California that was used as a main location was burned down by an arsonist shortly after production on this film wrapped.
When director John Stanley and his co-producer heard that Kerwin Mathews was working in an antique store in San Francisco, they approached him to play a swashbuckler in the movie within the movie. Kerwin loved the idea and said he would do it.