When determining who Batman's most terrifying villain is, a number of names typically float to the top. The most traditional answer would likely be the Joker, or perhaps one of Dark Knight's more horror-centric villains such as Professor Pyg or the Batman Who Laughs. According to one Batman writer, however, the answer to Gotham's scariest villain is none other than The Riddler himself.
Edward Nygma, a.k.a. The Riddler, first appeared in 1948's Detective Comics #140 by Bill Finger and Dick Sprang. One of Batman's classic gimmick villains, Nygma leaves a trail of riddles and clues to his crimes, providing the Dark Knight more of a mental challenge than a physical threat. In the current canon, Riddler served as Batman's first costumed villain through his takeover of Gotham during New 52's Zero Year. This event saw Nygma cut the power to Gotham City in an attempt to purge the uneducated and only allow the smart and resourceful to survive. After being defeated, Riddler carried his rivalry between himself and the Dark Knight to the present day, repeatedly engaging in (and losing) battles that challenged Batman's mental prowess.
Fresh off his recent sinister depiction in The Batman, Riddler returns to the page in Batman - One Bad Day: The Riddler in August. The 64-page single issue is part of a series of Batman - One Bad Day graphic novellas, named after Joker's notable philosophy from The Killing Joke and centered around the Dark Knight's greatest villains: Riddler, Two-Face, The Penguin, Mr. Freeze, Catwoman, Bane, Clayface and Ra's Al Ghul. The one-shots each have a different creative team behind the helm, with Tom King and Mitch Gerads working on Riddler's story. Tom King recently shared a variant cover for the comic by Mikel Janín on Twitter, and mentioned that he believes Riddler to be "Batman's most frightening villain."
It makes sense that King would consider the Riddler a terrifying threat given his work with the character. King's run on Batman during DC's Rebirth initiative involved the seminal storyline The War of Jokes and Riddles in which Riddler launches a war across Gotham with the Joker. This arc, set during early in Batman's career, showcases Nygma's sheer brilliance and power, revealing the extents to which he will plan and harm others to satisfy his own intellectual curiosity. King portrays Riddler as a man who can play others like pawns on a lark if he so wanted, with even Batman struggling to keep up. Currently, King's miniseries Batman: Killing Time involves Nygma as a primary antagonist as he leads Batman on a chase to recover a stolen item. This story again portrays Riddler as a major threat as he beats The Penguin within an inch of his life using his own umbrella. It's a shockingly violent moment from someone who is often treated in the Batman universe as a mere gimmick.
The Riddler has always provided Batman a mental challenge. Were he to abandon his obsession with leaving clues and puzzles for the Dark Knight to solve, there's no telling how far Nygma could go with his intelligence unencumbered. Writer Tom King promises readers will see a singularly scary side of The Riddler in Batman - One Bad Day: The Riddler, giving them the chance to see how he may actually be Batman's most terrifying villain to date.
Source: Tom King