Deepling
The deeplings are creations of the Bathybius, the vast layer of sentient water that occupies the deepest parts of Dadauar's oceans. In fact, more that that, they are literal pieces of the Bathybius, tiny slivers split off from its immense form and given independent existence. While the Bathybius itself is an amorphous puddle, however, the deeplings have definite forms--whatever forms the Bathybius chooses to give them. Some appear human, others like various animals; it's far from impossible for a deeplings to be in the form of an inanimate object. Some deeplings have the ability to change their shape, but this is not a power the Bathybius chooses to give most of them.
Whatever their shape, deeplings do have one thing in common. Like the Bathybius itself, they are made of enchanted seawater, and their appearance reflects that--they are completely colorless and transparent, with a watery sheen to their surfaces. This is a giveaway to the deeplings' true nature, but for deeplings that want to pass as other creatures there are ways to hide it through magic or through makeup, or even through something as simple as a hooded cloak. And many deeplings do just that--conceal their telltale transparency, and go about largely indistinguishable from humans, or from other creatures. Not all deeplings are interested in such subterfuge, however, and many go openly displaying their shimmery, glassy form, perhaps taking on weird and unnatural shapes to better flaunt their alien nature.
Deeplings vary widely in abilities and personality. They may all be ultimately pieces of the Bathybius, but the Bathybius is an immense and incredibly complex being, and it can choose just which of its abilities and which aspects of its mind it wishes to invest in a given piece. Thus some deeplings are big, dumb bruisers, efficient at physical combat but not at much else; others are skilled with spells and have formidable magical powers. Still others might be experts in some particular scholarly endeavor, or creative geniuses who create masterful works of art. With all the minds the Bathybius has absorbed and subsumed, it has no shortage of different talents and capabilities to draw on. Similarly, different deeplings are apparently created with different shades of the Bathybius's own enigmatic personality. Some deeplings are somber and humorless, others cheerful and mischievous. Some are noble and altruistic, others cruel and merciless. The possible variety in deeplings' capabilities and behavior is nearly limitless.
The common conception of deeplings is that they are servants of the Bathybius. Many, perhaps most, are just that. They are created by the Bathybius for specific missions, and when they are done they return to their progenitor to be willingly reabsorbed. Not that these deeplings provide any help in understanding just what the Bathybius's ultimate aims are, even if captured and interrogated--the deeplings possess only a tiny fraction of the Bathybius's knowledge and intellect, and know no more of its full goals than anyone else.
But by no means do all deeplings fit this mold. Many deeplings linger for years rather than carrying out short-term missions. And many deeplings don't seem to be carrying out the Bathybius's will at all. The deeplings that do serve the Bathybius do so voluntarily; they are free-willed beings, and if they carry out the Deepmind's will, it is because they choose to, not because it has any real control over them. But not all deeplings make that choice. There are many independent deeplings who go about their doings for their own purposes and not for the Deepmind's--though, given the latter's tremendous intellect and capability for subtlety, it's generally far from obvious which they are.
There are even some few deeplings who choose to openly rebel against their sire and try to fight against the Bathybius's mysterious plan. This fact suggests one of two possibilities: Either the Bathybius is not quite as sapient or as powerful as many believe it to be--it is fallible, and through either miscalculation or a lack of control does sometimes mistakenly create enemies to itself... or it's far more subtle and devious than it's often given credit for, and even those deeplings that think they're fighting against it are really serving its purposes in some way that even they aren't aware of...