The Redwall novels are full of these. Badredd's gang in Loamhedge and the group of vermin sent to hunt down Tagg in Taggerung are probably the most memorable and plot-influential.
In the Whateley Universe, Big Bad The Necromancer has put together a monster-themed gang called the Children of the Night. His Dragon Lycanthros is part of this gang, as well as Lady Darke, Nightgaunt, the Arch-Fiend, and the youngest and snarkiest of the group: Vamp. As of their second appearance, we learn that - in classic tradition for this trope - Vamp has been forced to join the gang and has been betraying them since before their first appearance.
The Wheel of Time: The Forsaken. They are only rarely played for laughs, but then, very little in this series is. There are 13 of them, and each served the Dark One for their own reasonsnote The thirteen Forsaken are, in rough descending order of power and threat level, Ishamael, Lanfear, Demandred, Graendal, Sammael, Semirhage, Aginor, Rahvin, Be'lal, Mesaana, Balthamel, Moghedien, and Asmodean; in the last book, they get a new member, Mazrim Taim, who receives the Forsaken name M'Hael. Ishamael was probably the only one who believes in the Dark One's agenda of destroying the world for all time; as for the rest, Asmodean did it because he wanted to be immortal, and some others joined because they were criminals, or in revenge for slights real or imagined by the Dragon (not to be confused with The Dragon). When the series began they were believed to be the most powerful channelers of all time, but after a few books we learn that some modern characters are on par with them or even stronger. In fact, they were just those of the Dark One's servants who happened to be with him when the Dragonsealed him away, and by now most of them have been killed. (And some have been brought back.) A lot of them were killed with surprise attacks, or by using an Artifact of Doom and the higher-level Forsaken (Ishamael, Lanfear, Demandred, and to a lesser extent Sammael, Semirhage, and Graendal) are far, far stronger than anyone else (and most of the others are less dangerous not because they're weak but because they suffer from Crippling Overspecialization, Evil Cannot Comprehend Good, and Chronic Backstabbing Disorder, which the heroes quickly learn to exploit). For example, Ishamael/Moridin can sense both Saidin and Saidar, while no-one else can sense his channeling.
Deltora Quest has the monsters guarding each of the gemstones. In order, they are a Black Knight, a giant carnivorous angler fish (who oddly enough has a taste for fine music), a demon witch and her deformed children, a giant three headed snake demon, a golem made entirely out of human skulls, a frog demon that oozes a powerful poison (the same poison the Big Bad's mooks use, in fact), a giant Extreme Omnivore slug demon, and finally a possessed illusionist who keeps demonic dogs as pets.
The Ten Who Were Takennote extremely similar to Wheel of Time's Forsaken, albeit generally better at living up to their reputations and made first, called Taken for short note The original Taken are Soulcatcher, the Limper, Shapeshifter, Stormbringer, the Howler, Moonbiter, Nightcrawler, the Hanged Man, the Faceless Man, and Bonegnasher; they worked for the Dominator and later the Lady, but neither of those are considered part of this group. As is typical for wizards in that setting, their names are descriptive - Soulcatcher steals souls, the Limper limps, the Howler howls uncontrollably, Shapeshifter changes shapes, Stormbringer controls the weather, and so on. Typically, they are extremely hard to kill; this is true of all wizards, who are longer lived and more durable than muggles, but the Taken are strong enough to be effectively immortal, and capable of recovering from pretty much anything short of total body destruction.
Later in the series another group is introduced — the Shadowmastersnote Longshadow, Stormshadow, Moonshadow, and Shadowspinner. They're not quite as dangerous, both because there's only four of them and because their leader, Longshadow, is a paranoid nutcase who isn't nearly as good at keeping them in line as the Dominator and the Lady did with the Taken, but they're still terrifying enough to conquer and terrorise the entirety of the Shadowlands. It's eventually revealed that Stormshadow used to be the Taken Stormbringer, giving her the dubious distinction of being part of both groups.
The Death Eaters from Harry Potter are Voldemort's henchmen. They have the same dress code, their own names, and some other factoid to them. Lucius Malfoy, Bellatrix Lestrange, Peter "Wormtail" Pettigrew and Fenrir Greyback are the most significant recurring Death Eaters; others such as Professor Quirrell, Barty Crouch Jr., the Carrow siblings, and Yaxley have significant roles in one book, and there are number of others (Rookwood, Avery, Dolohov, Rowle, etc.) who are namedropped/show up often, but get little development.
From Worm, we have the Slaughterhouse 9. As the S9 are labeled as an S-Class Threat, they have a standing kill-order placed on the group as a whole, applicable to new members as well. As such, they have a high turnover rate. Their leader, Jack Slash, mentions that there are few that he considers "long term members," which includes himself, Bonesaw, and the Siberian. He also mentions that Mannequin was a borderline case, as he had been with the group for a very long time.
Moribito: Guardian of the Spirit: The Hunters hound Balsa and Chagum's steps for most of the story and serve as the main physical threat from the Mikado's Court. Ultimately, as the story ends up with all human characters on the same side, they help Balsa defend Chagum in the climax and help shoot down the Emperor's plan to have Balsa assassinated.