Villainous pets come in different flavours. When the villain's pet is mostly sedentary and largely does not play an active role in the plot, you have a Right-Hand Cat. When the villain's pet is an active fighter/guard against the heroes, you have a Right-Hand Attack Dog.
When the villain's pet is the key reason why he is a threat in the first place, you have a case of Villain Holds the Leash. Whilst the pet is only obeying its master's orders, its presence greatly increases the villain's threat level. Maybe the pet has some sort of ability that is crucial to the Evil Plan. Maybe the villain needs its presence to keep his human minions in line. Or maybe their master is simply a Non-Action Big Bad who needs the beast as muscle. In a nutshell, whilst the human villain is the one giving the commands, the pet is the main antagonistic force in the plot.
This can vary from an Evil Overlord with a dragon, a Mad Scientist with a genetically engineered monster, a Corrupt Corporate Executive Rich Bitch with a Mister Muffykins to a street gang with an Angry Guard Dog. The defining factor of a case of Villain Holds The Leash is that, without the pet, the master is much less of a threat. The pet is the main asset in the villains' operation - with its defeat, their powerbase decreases significantly and they are far easier to dispose of.
Exactly how the villain ended up holding the leash varies. Sometimes, the pet is loyal to the villain - often ferociously so - and serves them of their own free will. In other cases, the pet's loyalty has been forced, either through abusive treatment or through mind control by either magical or scientific means. If it's any of the latter two instances, expect the attack dog to turn on its master, either killing them or abandoning them to their fate once freed of their control.
See also Shark Pool (where the villains' pet is mostly sedentary), Action Pet, Kid with the Leash, Fluffy Tamer and especially The Beastmaster and/or Squishy Wizard, whom these kinds of villain usually tend to be.
- Through out the Pokémon anime, quite predictably due to the Mons premise, most bad guys' threat level depends on the power and skill of the Pokemon they have. Most main arc villains' schemes involve them taking control of a powerful Pokemon as muscle for their plans. Team Rocket, due to having Pokemon as bungling as they are, are generally the show's Ineffectual Sympathetic Villains, though anytime they can direct them competently or temporarily get hold of a more dangerous Pokemon, they often become Not So Harmless.
- In the Godzilla (IDW Publishing) comics, there are multiple cases of this, as per the franchise's tradition.
- Battra and Rodan serve as Minette and Mallorie's attack dogs in Godzilla: Kingdom of Monsters. There's also a rare heroic case of this trope in the US Government and Mechagodzilla.
- There are multiple cases of this kind of villain in the different arcs of Godzilla: Rulers of Earth - overall, Gigan acts as the main asset in the arsenal of Rhizon's faction of Cryog.
- Destoroyah, Titanosaurus, Manda and Gezora serve as the Devonians' main weapons in the first arc - Destoroyah in particular, is their strongest kaiju, being so powerful that he manages to nearly kill Godzilla. For the Cryog, Gigan is joined by Orga.
- The Mechagodzilla army and Mecha-King Ghidorah serve as the primary weapons of Rhizon and Minette and Mallorie in the second arc. Once Minette and Mallorie are abandoned by Rhizon, Battra serves as their main weapon once more.
- In the concluding arc, the Trilopods (especially Magita) serve as the primary weapons to the Cryog Emperor Karkaro - their threat is so great that all of Earth's monsters have to ally against them.
- A bizarre example (where the "pets" in question are fully sapient) occurs in Dinosaur King: Retold. Throughout Season One, the Alpha Gang's dinosaurs repeatedly demonstrate that they are far more intelligent, competent and dangerous than their human partners - and it's made clear that they are only working with Dr. Z because it better suits their own agenda.
- In "The Devils Here", the second part of the finale arc of Prehistoric Earth, whilst the Novum board's black-ops squad are technically the main antagonists, it is the young female T-rex that they have released in the park that is the primary threat.
- In a heroic example, it is unclear how the park staff could have stopped the mass breakout or Frank and Percival's scheme without the allosaurs Drogon, Rhaegal and Viserion.
- Professor Ratigan, archnemesis of Basil of Baker Street in The Great Mouse Detective, uses a bloated cat named Felicia as his primary enforcer, using her to threaten Mr. Flaversham into co-operating, attempting to kill the Mouse Queen, and to keep his minions in line - often feeding her underlings who disappoint him, such as unfortunate Bartholomew and, very nearly, Fidget.
- In How to Train Your Dragon 2, Drago's Bewilderbeast, as well as providing muscle for him, is an integral part of his plans, due to its ability to control dragons. Once Toothless breaks free of its control and becomes the new alpha, Drago's plans fall apart.
- Marcel and Nigel from Rio are a downplayed case. While Marcel still drives the plot to some degree, Nigel is the main asset of the bird-smuggling operation and is far more effective than his master's human lackeys; in particular, he is the lynchpin of the break-in at the that allows the smugglers to capture Blu and Jewel.
- In Alice in Wonderland (2010), most of the fear that the Red Queen inspires is because she has control (or some agreement) over the Jabberwocky. After it is slain, her minions (including her Dragon) desert and she is easily deposed.
- In Brotherhood of the Wolf, the eponymous society have this relationship with their Beast, a lion they abusively trained, which they use as their main weapon in their plan to undermine public confidence in the king and restore the old ways to France.
- This trope is common in Godzilla films. In many films, the villains have taken control of a giant monster in order to Take Over the World, and the main objective of the heroes is often to help Godzilla defeat the monster, or to destroy the villains' control over the monster. Here are some examples:
- King Ghidorah often served this kind of villain - the Xilliens in Invasion of Astro-Monster, the Kilaaks in Destroy All Monsters and Wilson and Grenchko in Godzilla vs. King Ghidorah. In Godzilla vs. Gigan, Ghidorah is joined by Gigan in serving the Space Hunter Nebula M Aliens.
- Mechagodzilla is almost always used by this kind of villain, starting out as the main weapon of the Black Hole Planet 3 Aliens in Godzilla vs. Mechagodzilla and Terror of Mechagodzilla. In the latter, he is joined by Titanosaurus. In Godzilla vs. Mechagodzilla II and the Kiryu dulogy, he serves as the main weapon of the JSDF.
- The Xiliens in Godzilla: Final Wars control many monsters, but Monster X is the strongest of them.
- Alan Jonah and Emma Russell attempt to be this for King Ghidorah in Godzilla: King of the Monsters (2019) and to a lesser extent the other Titans. Unfortunately, King Ghidorah turns on them and awakens the Titans for his own purposes and they can't do a damn thing to stop him.
- In The Brothers Lionheart, the warlord Tengil is dangerous enough due to his regular troops, but he is made unstoppable by his control over the dragon Katla.
- Guards! Guards!: Lupine Wonse intends to be this kind of villain, secretly summoning a dragon to wreak havoc, finding a suitably heroic-looking schmuck to serve as his Puppet King by unsummoning the dragon to "kill" it. Unfortunately, the dragon proves to be sapient, very angry at being used in this way, and forcing Lupine to serve it while it takes the throne as king (well, queen) after un-unsummoning itself and eating the "hero".
- In Harry Potter and the Chamber of Secrets, whilst Tom Riddle in the Diary Horcrux is the Big Bad and Lucius Malfoy is the mastermind behind the plot to open the Chamber of Secrets, it is the chamber's basilisk who serves as the story's main antagonist, with the story ending with Harry defeating it.
- Dragons served as the main guarantor of the Targaryens' power for most of their dynasty's reign in A Song of Ice and Fire, due to their Fantastic Nuke status. Rather sadly, this meant that they never built up any form of institutional bureaucracy which would give them power independent of the dragons. After the dragons died out, the Targaryen dynasty went through a downward spiral that culminated in its end.
- Tod Robbins' short story "Spurs" (on which Tod Brownings' Freaks is loosely based) has the Villain Protagonist dwarf owning a very large, fearsome dog, which he rides atop as part of his "errant knight" gimmick in the circus sideshow. Said dog is 95% of how he coerces the bareback rider Jeanne-Marine into staying in an abusive marriage with him.
- Game of Thrones: Zig-zagged with Daenerys and her dragons (especially Drogon). Whilst Daenerys had already gained the loyalty of the Dothraki and the Unsullied before they were big enough to be weaponized, once the dragons are weaponized, her military power increases considerably, allowing her to curbstomp armies and destroy cities with ease.
- Primeval: Oliver Leek, Series 2's Big Bad has a Praetorian Guard of Future Predators who he controls using a neural implant. When Cutter short-circuits the implant, they rip their former master to shreds and he can't do a damn thing to stop them.
- The Whisperers from The Walking Dead are not exactly harmless, but in a fight they're mostly reliant on sneakiness and guile; their zombie disguises allow them to blend in with a crowd of zombies and then catch opponents by surprise. Without this tactic, most members have the fighting ability of an average human armed with a kitchen knife. What makes them truly dangerous is the half-trained herd of thousands of zombies that they can steer towards their enemies.
- In the Jonny Quest episode "The Dragons of Ashida", Dr Ashida uses the titular genetically enlarged giant lizards as his personal attack dogs, controlled by his bodyguard Sumi. When the lizards (and Sumi) turn on him at the end, he's powerless to stop them.
- In the Kim Possible half-episode "Roachie", the villain takes control of a horde of giant mutant roaches. The roaches themselves are benign when left to their own devices; in fact, Ron made friends with one of them.
- In the SpongeBob SquarePants special "Dunces and Dragons", much of the fear the evil wizard Planktonamor inspires is due to the fact he has a gigantic dragon jellyfish under his control. When it turns on him at the end, after being shown kindness by SpongeBob, he is powerless to stop it.
- The Decepticons initially have this relationship with Predaking, an ancient Cybertronian cloned from fossilised remains in Season 3 of Transformers: Prime, and plan to clone more like him. However, when he turns out to be sapient, they begin to have second thoughts and terminate the remaining clones, leading to him turning against them, massacring a good portion of their troops and almost defeating Megatron in battle.