Mr. Sardonicus is known for two things: influencing the look of the Joker and having one of those crazy William Castle gimmicks. In this case, the audience was supposed to vote on what ending they wanted to see. Of course, there was really only one ending, because the vote was "Do you want Sardonicus to suffer even more... or do you want to show mercy?" Obviously, everyone wants the suffering.
The movie itself is a lot like Dracula for the first hour or so, except that instead of Jonathan Harker, they've got a brilliant doctor who specialized in paralysis cases. But Sardonicus (who's really a Baron, not a Mister) turns out to be not a vampire but a crazy guy with a permanent crazed smile on his face. It's creepy, but I don't think it's as creepy as the mask he normally wears. The unmoving face works well with his snooty attitude.
Anyway, it's a perfectly acceptable cheapo scare movie.