Plasmid

The sahuagin dominate the Thunder Sea. Proud and predatory, the sahuagin see the creatures of the surface world as primitive and weak. The sahuagin are generally content to ignore the lesser creatures that dwell above the water, but when there is blood in the water, they are implacable and deadly foes. Through magebreeding and induced mutation they have created a host of terrors, such as the duplicitous malenti, the four-armed Sahuagin Barons, the shape-shifting Plasmids, and the terrifying Sahuagin Claws of Sha'argon.

Plasmids are shape-shifters, magebred by the sahuagin of the Thunder Sea using mimic stock infused with the ichor of the dreamers. Plasmids serve both as deadly guardians and living tools, reshaping their mutable bodies to serve the needs of their sahuagin masters.
Skin of Stone and Steel. A plasmid can change the texture of its flesh as well as its appearance. In addition to making the plasmid resistant to injury, this allows the creature to assume many functional forms. A plasmid can serve as a door with no lock or a chest with no lid, creating an obstacle that can only be opened by killing the plasmid. Plasmids can also be trained to assume shapes that serve as functional tools. A plasmid can become an alchemist's lab or a smith's forge, providing all the elements needed to pursue a trade. While this allows the plasmid to "serve as a tool," the plasmid remains a Large creature; it essentially becomes a workbench, with individual smaller tools connected to the primary mass by fibrous strands.
Loyal Servants... For Now. Plasmids possess a passive form of telepathy that allows them to sense the commands of nearby sahuagin. While they are conscious, they have a limited sense of self and no desires beyond service. At least, that's how they were designed and what the sahuagin believe. But it might be possible for a plasmid to develop greater intellect and independence—or for the plasmids of a city to be shaped by the desires of the local dreamer.