The Dark Knight has one of the best and deepest rogues' galleries in the superhero genre. While the Joker tends to take up most of the limelight when it comes to prominence in pop culture, it's easy to look through the list and find others that serve as great adversaries to Batman.
It's a wide variety of supervillains, with many ranging from the grounded, crime-noir realm and others that venture more into science-fiction and the supernatural. Similarly, some of these underrepresented villains also pose as one of Batman's biggest challenges in of physical and/or mental prowess.
Hugo Strange
Hugo Strange is one of the supervillains that hasn't gotten much time in the spotlight considering how threatening he can be. He has appeared in some episodes of Batman: The Animated Series, but arguably his most noteworthy role was as the "red herring" main antagonist of Rocksteady's Arkham City video game. Strange is a psychiatrist who is using his impressive brains in unethical and lethal experimentation.
His defining characteristic is his obsession with Batman and how the machinations of his mind work. Unlike Jonathan Crane/Scarecrow, it isn't fear that drives his methods, rather, it's the trauma of the Dark Knight's psyche. Strange is fixated on Batman as a fascinating, wild specimen and obsessed with suring him. Ultimately, he wants to beat Bruce Wayne at his own game and mold his warped idea of a "perfect" Batman. He's arguably the best Batman comic villain to not yet be prominently used in live-action.
Lady Shiva
Among other things, one of Batman's best assets is his mastery over countless forms of martial arts and the physique to back that up. However, Lady Shiva is one of the few villains in his rogues' gallery to be able to defeat the Dark Knight in hand-to-hand combat -- and on more than one occasion. As such, she easily established herself as one of DC Comics' best canon martial artists.
In the comics, Shiva leads the terrorist organization that split from Ra's al Ghul's original League of Assassins. The head of the League of Shadows is known to be even crueler and more extreme than the former, creating a cold origin story for her daughter (and Bat-family member) Cassandra Cain. With this daunting reputation and combat prowess, Lady Shiva makes a strong case in favor of more frequently featuring as the main antagonist of a Batman story.
Calendar Man
Along with the likes of Mr. Freeze, Calendar Man was one of several Batman supervillains to feature as joke characters in early comics. Thankfully, though, he received a thrilling revitalization in 1996's The Long Halloween comic arc. Julian Day went from wearing a comedic calendar-themed spandex suit to being a chilling serial killer.
That comic wrote him exceptionally well, using Hannibal Lecter-inspired character traits. Seeing Batman's interactions with him in trying to deduce the Holiday Killer's identity were cold, tense scenes, and his more direct villainous role in the sequel, Dark Victory, was even more satisfying. David Dastmalchian's portrayal in the animated adaption of the comic was also well-executed. He certainly has a gimmick comparable to Riddler, but the specific serial killer archetype makes Calendar Man sufficiently unique from him.
Deathstroke
Similar to Shiva, Slade Wilson/Deathstroke is another physically formidable foe for Batman. He originally featured as a villain specifically to the Teen Titans, gaining more popularity later in the Cartoon Network show. However, he naturally bled into Batman's part of Gotham City specifically, which makes for some more thrilling encounters.
Deathstroke is a contract mercenary, with the Caped Crusader himself being Slade's most elusive attempted hit. The DCEU nearly featured him in a major capacity, but the theatrical franchise's turbulent track record seems to have put those plans on ice. Aside from CN's aforementioned Teen Titans cartoon, another one of Deathstroke's most prominent roles was in WB Games Montréal's prequel game, Arkham Origins. He's also many fans' pick for Origins for being such a great boss fight.
Clayface
Basil Karlo's Clayface can be argued as being one of the underrated "big" villains in Batman's catalog of rogues. He's an easily recognizable character but tends to get minimal exposure across the different mediums. It's easy to simply slot the character in as a generic "movie monster" role, but Karlo's backstory makes for something that can be more intimate while retaining the horror elements. It's a "tragic villain" angle similar to that of Mr. Freeze once he was reinvented in Batman: The Animated Series.
The man raised to put on an act and achieve Hollywood fame makes his affliction all the more thematically fitting. Another interesting angle that Clayface has had was in DC's Rebirth-era run of Detective Comics by James Tynion IV. Karlo becomes rehabilitated and turned into a hero and member of the Gotham Knights. His character arc throughout that storyline was genuinely touching and made his redemption feel earned.
Ventriloquist & Scarface
While the Ventriloquist and Scarface personas are separate identities, they come as a package deal in Batman stories. In this case, Ventriloquist (Arnold Wesker) is a timid man suffering from dissociative identity disorder, projecting a mob boss persona onto the puppet Scarface. He appeared in a ing role in one of the best episodes of The New Batman Adventures, painting him as a much-needed success story in Gotham City.
Arnold successfully rehabilitated in Arkham Asylum and was discharged, with Bruce Wayne promptly setting him up with a good job at Wayne Enterprises and an apartment. The conflict arises when Batman discovers and stops "Scarface's" old gang returning to try and force Arnold into relapsing. Branding Ventriloquist specifically as a "villain" could be a technicality, as Wesker himself in the show demonstrated that there's a good man underneath the trauma.
