The Monster Manual describes a humunculus on p188.
A homunculus is a construct that acts as an extension of its creator, with the two sharing thoughts, senses, and language through a mystical bond.
If I were to find a way to create one, could it be turned against me?
Fortunately it is immune to the charmed condition, which eliminates many threats. But is there some way control of the homunculus could be seized by someone else, and it could be caused to act in a way contrary to the control normally exerted by its creator?