In addition to the characterization of Hyde (particularly the repeated mention of deformity), Stevenson uses setting to help create a sense of evil. Check out the description of the back of what we learn is Jekyll's residence just before Enfield relates his story to Utterson; or the description of the night of the Carew murder. Surely Stevenson gives us a full moon so that the maid can identify Hyde, but a full moon often suggests something sinister.
Further, Stevenson uses events in the plot to suggest evil and foreboding--for example, the description of Hyde trampling the girl; the description of the confrontation between Hyde and Carew; the discussion between Jekyll and Utterson prior to the Carew murder; Dr. Lanyon's narrative; the incident at the window; and certainly Jekyll's full statement. Since the depravity and evil of human nature is so central an aspect of Stevenson's theme, he uses all of these and, of course, more to create a sense of evil in the story.
The author creates tension and evil with the creation of Edward Hyde, the product of Dr. Jekyll's experiment.
"The Strange Case of Dr. Jekyll and Mr. Hyde is based on the story of Edinburgh's infamous Deacon Brodie, who was discovered to have been living a double life, coupled with a dream Stevenson had one night, what he called "a fine bogey tale," about a man who drinks a potion made from a white powder and subsequently transforms into a devilish creature."
Suspense is also felt in not knowing what Mr. Hyde, who is a totally immoral individual, will do once he emerges and takes control of Dr. Jekyll. Hyde is unpredictable and violent.
Edward Hyde reflects the ugly side of the human spirit. He embodies evil with such ease, it is very frightening to imagine a killer more manipulative, sadistic and indifferent that Hyde. He represents the dark passions that exist in all of us, except in Hyde's case they are in total control of both mind and body. What is really eerie, is that Jekyll finds himself enjoying his alter ego's escapades.
"Part of him as Hyde "felt younger, lighter, happier in body" and more free than Jekyll ever had, while at the same time he recognized this new creature as "pure evil." Jekyll continued taking the potion until one night he found himself transforming without the drug and noted that Hyde was getting stronger."