Sableine

A race of Mother's children. For the most part they're tall and thin humanoids with dark skin and ink-black hair. They generally congregate in groups, and you can often know sableine are nearby because of the presence of a flower by the same name - sableine plants have veins so dark they're nearly black and black-edged lily-like flowers.
Sableine are one of the oldest of Mother's children. Their function is to be breeders. They consume all types of magic, and they use that magic to reforge genetic material. Sableine can theoretically breed with any of Mother's children, though they are quicker and easier at races they know best. Anyone may go to a sableine and offer some of their genetic material in return for attempts at children. Sableine will consume the material and use their inborn magic to learn how best to match and rearrange it to create the next generation.
For penis-having or equivalent supplicants, the process is much like normal sex. They ejaculate into the sableine (who usually have cavities matching what the race would expect), and the sableine develops embryos inside themself. Flawed embryos will be purged fairly early on, so depending on sableine familiarity with the race it may take multiple attempts before a viable child results.
For vaginal supplicants, it's a bit more complicated. Ovulation cannot be guaranteed, and even if it could eggs are more vital than sperm and experimentation would have too high of a toll on future fertility. Instead, the sableine will consume larger amounts of genital fluids to start to learn the patterns, and if an egg is found the sableine will replicate it inside themself enough times that experimentation can be run. If an egg cannot be found quickly, sableines will simply attempt trial and error. They will inject what they believe to be the closest genetic material to the supplicant in hopes of impregnation happening. If sableine have already had an experience with a penis-having member of the supplicant's race, then as soon as the genetic material is recognized impregnation is almost assured.
Penile supplicants are more common due to reliability, and sableine magic has a particular quirk in that case. Due to their ability and willingness to genetically rearrange an embryo they carry, the resulting child has genes farther from the supplicant than normal. A child born to a sableine is genetically more like a cousin or grandchild than a full child, which greatly helps spread the gene pool. This is the main reason that sableine are so vital - when a new race emerges, there are usually only a single digit number of individuals of that race born. The first two generations of a new race breed almost exclusively with sableine to ensure that their genetic spread is wide enough to prevent future problems.
A sableine-bred child has many benefits over a normally conceived child. Sableine do not pass on genetic illnesses either physical or mental, so unless something is inherited from the mother a half-sableine is generally much healthier. Sableine also do not pass on their own traits to children. A half-sableine child will look nothing like the sableine parent, only a shuffled/modified version of the normal parent.
Half-sableine children inherit an invisible advantage, though. Any half-sableine can breed successfully with any race their sableine parent knew. A half-sableine wildling, for example, can breed with magin, centaurs, mermaids, etc. successfully, though at a low rate. The resulting children gain nothing from the non-sableine part of their parent, though. In the case above, the child resulting from a wildling and a centaur would be half centaur, half sableine. The genetic shuffling also would not happen, meaning that the resulting child would be almost a genetic clone of their parent.
In the situation where both parties are half-sableine, genetics become slightly more complicated. For example, a half-sableine mermaid breeding with a half-sableine wildling has a few possibilities. The first corner of the square, half-mermaid half-wildling, is not viable and will not even reach the fertilization stage. Half-mermaid half-sableine and half-wildling half-sableine are both viable, though depending on the species of the carrier it may be stressful on their body to carry a species not their own. The last square of possibility, half-sableine half-sableine, is impossible to carry to term. Pregnancy may happen in this case, but it will invariably be aborted fairly early on. The only way for a full sableine to be born is to a full sableine.
Due to the half-sableine part passing invisibly yet fully to a child, it's nearly impossible for a mother's child whose parents are the same race to know if they are half sableine without simply trying. "Proving out" sableine blood is a common practice, particularly among royalty that may need to marry outside their race for treaties.
Sableine share genetic patterns with each other through touch. Using this, they can share methods that work for different races so that each individual sableine doesn't have to repeatedly try different things. Sableine mimic what they see, so they often hug and kiss each other, or cuddle up in piles.
Although many people who have not met sableine consider them to be a type of flower nymph, the truth is that sableine are shapeshifters with a tiny strain of telepathy. They can instinctively sense what forms their supplicants are most likely to find appealing, and their forms are fluid enough to accommodate any possible race both sentient and nonsentient.
Motherborne individuals naturally attract sableine. Even if they do not seek them out, sableine will find them and attempt to instigate mating.
Sableine do not often eat. For the most part, water and magic are all they need to sustain themselves. If they lose too much mass through repeated birthing, they can consume plant matter to grow back to their normal size. Sableine life cycles are fairly short, with individuals dying off naturally around twenty or maybe thirty years old. The sharing of genetic information ensures that little is lost, though, and a sableine needs no mate to replicate themself. Any time they choose to, they can birth a clone of themself.
The killing of a sableine is anathema to any of Mother's children, though protection of them is not necessary. A natural death is a sad occurrence, but not a monumental one.