In the early days of production, another project entitled "The Angel of Terror" (an original Edgar Wallace novel title) was intended to become the 25th Fflm of the series. The film was to be a West German-British co-production directed by Harald Reinl (it would've been his sixth Wallace film and his first in color). Due to the financial trouble of the British co-producers and scheduling conflicts of Reinl, who was directing Death and Diamonds (1968) at the time, the project was abandoned.
In the English-dubbed version, when Edgar Wallace 's name appears on the screen, a voice says, "Hello. This is Edgar Wallace speaking." The real Edgar Wallace died in 1932 while in the US working on a film that would become King Kong (1933).
Italian censorship visa #52043 delivered on 7/30/68.