Deena Fear is the main villainess of "The Dead Boyfriend", the 5th book in R.L. Stine's revived Fear Street series (published on September 27, 2016).
Deena was a member of the infamous Fear family, known for their horrifying past and numerous scary legends centered around them. She was a mysterious Goth who possessed supernatural powers. She also had a romantic fixation for new Shadyside High student Blade Hampton and became jealous when protagonist Cathy-Ann (though throughout the book, she calls herself Caitlyn) began dating him. After warning Cathy at a party she went to with Blade that he was hers first, Deena used her powers to fuse her bracelet onto her wrist, subtly threatening her later on at work.
When both Cathy and Deena found out that Blade was cheating on Cathy with another girl, catching the two at a club, Deena tried to confront an upset Cathy. Cathy rejected Deena and ran away, later confronting Blade at his house. It was then that the evil Deena (who had followed Cathy) used her powers on Cathy to make her stab Blade to death with the knife Cathy had been keeping her bag following a robbery attempt. Later on, though, Deena wanted Blade back and decided to use her powers to bring him back to life, believing that she could get Blade to be with her after she did so.
While her attempt to bring Blade to life at his funeral appeared to fail at first, it succeeded in bringing Blade back to life. The undead Blade then began terrorizing Cathy, wanting her to join him in death. Despite her fear of Deena, Cathy eventually turned to Deena for help in getting rid of Blade. Cathy visited Deena at her house and witnessed more of Deena's psychotic antics, including keeping two taxidermied bodies in glass cases in a room (claiming them to be her parents) and demonstrating her powers by drowning her pet parrot and bringing it back to life. She also confessed to having used her powers to make Cathy murder Blade, which made Cathy weary to trust Deena. But after being further tormented by Blade to the point where her family and friends became convinced she was unwell and she accidentally killed a man she mistook for Blade, Cathy returned to her. But when Deena tried to use Blade's dead hand (him having lost it while attacking Cathy) to make him dead again, she failed and told Cathy her only option was to kill Blade again.
Near the end of the book, Cathy was being attacked by Blade outside her house when Deena arrived, watching as Cathy stabbed Blade repeatedly until he was subdued. Deena took Blade's body and assured Cathy that she would take care of everything. But instead, Deena (for unknown reasons) either brought Blade back to life again or allowed the potentially surviving Blade to continue to walk among the living, as evidenced by Blade appearing at Cathy's book signing (having published her diary after claiming to her parents that the events she documented in it were a fictional novel). Deena's official fate was never revealed.