One of the most interesting but least used (in my experience at least) types of monsters is the automaton. Mechanical constructs have a long real world history and, if not quite as magical as their creators would have liked the certainly captured the public’s imagination.
Among the most famous automatons is the Mechanical Turk. Build by Wolfgang von Kempelen to entertain the Austrian Empress Maria Theresa in the second half of the 18th century. It would defeat a variety of opponents including Napoleon and Benjamin Franklin. It was only after 50 years that it was show to be a fraud in 1820. The elaborate desk that held its table had a concealed human operator within. It was captivating enough that it would continue to be shown up until its accidental destruction by fire in 1854. It’s owner at that time was Dr. John Kearsley Mitchell. Among Dr. Mitchell’s other claims to fame he was Edgar Allen Poe’s personal physician.
It was succeeded at least two more machines, Ajeeb and Mephisto. The later was remote controlled instead of having an operator. A true automaton capable of playing chess on its own would not appear until 1912 with El Ajedrecista. Even then, it was limited to three piece end game of its own king and rook against a human king.
The Turk, or, better yet, a truly self-actuated version powered by magic, would be a great addition to a campaign. A court magician could have created one for his king’s entertainment. From there plots from the Turk as evil adviser, rival of its creator, or test of potential advisers or employees only scratch the surface. I can see two uses of the Turk in a dungeon. He could be an encounter of his own, perhaps a trap of some kind or a way to gain information. He could also constitute an item of treasure. I find this later idea deliciously old school in the ingenuity players would need to see it as treasure, retrieve it, and find a way to make us of it in the outside world as well the interested parties the later would create. These traits are increased if your campaign eschews the traditional medieval setting for something slightly more modern as LotFP is moving towards (perhaps it could be the key focus of high level players’ inn) or my own World After.