The Flash recently ended and with that comes the end of the Arrowverse. Here are the best Arrowverse Villains.
Reverse Flash The Flash (Tom Cavanagh/Matt Letscher)

Reverse Flash is The Flash’s (Grant Gustin) greatest enemy. Matt Letscher and Tom Cavanagh got to play Reverse Flash and both added something different to the role. Reverse Flash was a thorn in The Flash’s side throughout the run of The Flash.
Damien Darhk Arrow (Neal McDonough)

Damien Darhk is complicated. He was first introduced in Arrow and was a wicked man. After being killed on Arrow he resurfaced on DC’s Legends of Tomorrow. He stuck around for a few seasons and another side to him was revealed. He wasn’t as bad as he once was. Damien is one of the strongest villains to have been on Arrow. He was also a big threat since he had powers. All prior villains up to that point did not have abilities.
Joker Batwoman (Nick Creegan)

Marquis Jet was Ryan Wilder’s (Javicia Leslie) brother. He was introduced in Season 3 of Batwoman. Ryan found her birth mother and brother. Season 3 took a turn when Marquis became the new Joker. The rest of the season focused on the Joker vs. Batwoman. Marquis would have made The Joker proud. Marquis met The Joker years ago which is what led to Marquis following in his footsteps. The Joker is definitely a memorable villain from Batwoman.
Lex Luthor Supergirl (Jon Cryer)

Lex Luthor finally made his debut on Supergirl in season 4. He went to appear throughout the series until the end. Lex was maniacal and funny. Lex was everything. He tipped the scales in his direction every time. He got to play a role in Crisis on Infinite Earths. He even found some romance in the final season. Lex was unpredictable and the only thing predictable was that Jon Cryer was going to give quite a performance.
Malcolm Merlyn Arrow (John Barrowman)

Malcolm Merlyn, also known as the Dark Archer, played a major role on Arrow for 5 seasons. He went from bad to good and switched sides on several occasions. He is one of the best villains of Arrow and he also was the OG.
Alice Batwoman (Rachel Skarsten)

Alice was a main character on Batwoman for its entire run. Alice was the Joker to Kate Kane’s (Ruby Rose) Batwoman. Alice and Kate were sisters which added a different dynamic to the mix. Kate Kane left the show. She was presumed dead. Alice eventually reunited with Kate (Wallis Day). Due to all the crimes Alice committed she was sent to prison. Eventually she was forced to work with Ryan Wilder and Team Bat to help stop other villains in Gotham. Alice is one of the best villains from Batwoman.
Prometheus Arrow (Josh Segarra)

Adrian Chase was a psychopath. Once he was revealed to be Prometheus, things kicked up a notch. He was so bad that The Green Arrow had to enlist help from Malcolm Merlyn and Slade Wilson. Prometheus was a cool villain and had a cool reveal when he was unmasked.
Deathstroke Arrow (Manu Bennett)

Slade Wilson was seen in flashbacks in season 1 to Oliver’s time on the Lian Yu. Slade was presumed dead. In Season 2 it was revealed that Slade was really alive, and he wanted revenge on Oliver. Deathstroke put Starling City in danger and murdered Oliver’s mother Moira Queen (Susanna Thompson) in front of him and his sister Thea (Willa Holland). Slade went on to appear from time to time on Arrow after season 2.