Big Bad Pet

A Giant Mook that's usually an animal, or any non-human (commonly referred to as a "creature") for that matter, who is kept by the Big Bad as a pet.

Often too large or wild to be in the Big Bad's main quarters, the Pet is usually kept in a cage, cavern, dungeon, or any other secluded place. The Big Bad Pet's job is usually to guard the Big Bad's lair, or to viciously consume the hero once the latter is thrown in a pit of death. It's usually too dumb to actually be given orders, so it sort of serves as a Personal Mook for the villain.

To elaborate, Big Bad Pets are, well, big and bad. They usually are composed of dragons, snakes, sea monsters, giants, lions, bears, big hungry dogs, sharks, giant man-eating plants, and the like. They're the creature version of The Dragon, only usually much larger and of savage nature. Thus, they usually don't get that much character other than growling about to frighten the protagonists.

Film

 * Jabba the Hutt kept a pet rancor in Return of the Jedi. (Wookieepedia says that its name was Pateesa.)

Literature

 * Bill Sikes kept his attack-dog Bull's-eye by his side for most of Oliver Twist. Bull's-eye was shown to be vicious, and helped add to Sikes' menacing nature.
 * While not a "Big Bad" by any stretch, Hagrid Kept a number of dangerous beasts throughout the Harry Potter series, some of which would fall into this category.
 * Fluffy, a large, three-headed dog is used as a guard dog in Harry Potter and The Philosopher's Stone due to it attacking people indiscriminately.
 * Aragog the giant in The Chamber of Secrets meanwhile serves as more of a "pit of Death" variety, as he and his numerous offspring will happily devour anyone approaching their nest in The Forbidden Forest.