Bobbie Bresee revealed on the commentary of the BCI DVD release that she received some possessed voice coaching from Mercedes McCambridge (notable for the demonic voice in The Exorcist (1973)) while co-starring with her in _"Charlie's Angels" (1976) Angels in Springtime_.
The scleral contact lenses that Bobbie Bresee had to wear during some possessed scenes damaged her eyes. This damage resulted in her filming some scenes towards the beginning of the film without her eyesight.
When BCI Eclipse obtained the rights to release Mausoleum on DVD, they could not find any original elements to transfer. This means the original elements either no longer exist or are temporarily lost. BCI was forced to use a damaged print instead for the DVD release. Because of the damage, BCI decided to release it as a double feature instead of a single release as they first planned.