First off, the summary is inaccurate. Satan doesn't save the man's life, the man becomes a spirit of evil that inhabits people and awake the latent evil in those around him.
Second, having seen this movie and all of the episodes of SCTV with Mary Charlotte Wilcox, it is obvious these are two different actresses. Shape of the face, eyes, their voices, everything is different. Also, no one else but Mary Charlotte Wilcox could be Idela Voudrey and that includes this Mary Wilcox.
I like this movie for some reason. It tends to get a little slow but it actually has a nice sort of message at the end when Langdon finally meets his fate, something he longed to experience for decades as a spirit of evil.
John Ashley stars and he seems like he is doing a kind of Elvis impersonation at least with the hair when he isn't the beast. Satan transforms him into a murderous creature put of punishment because of his desire to be an individual again. A temptation that strikes him when the devil allows him to inhabit this man with his own face. The change causes him to lose focus on ruining the people around him to trying to spare them that pain. It could have been more than just a monster movie but it tries....