What are Shadromancers?
Shadromancers are pretender species, represented by core spark and black materia units,
who came from mysterious place named Shado and took their start as a nightmares or night guests.
First shadromancers were summoned into different worlds by physically and mentally weak persons. Such persons searched help and protection in shadromancers, and shadromancers realized, that this is perfect variant to get as much attention as they need to live happily without starving. However, their race splitted into two due to different decisions:
 more wild ones, who decied only take something from others and fright them to death, became animal-like Bit-thing-Beasts
 more social ones, who decided to became to others close friends and share all with them, not letting them die to get an endless source of food, saved their mind and started to change themselves to be less frightful to hosts.
Do they have any special powers?
They can change their appearance by their own will and travel between different worlds. However, outside of Shado they can be seen only by their hosts/ward-dreamers or other shadromancers.
Despite the fact, that they can change themselves into any shape and form, they usually use human bodies. When their bodies are heavily damaged, they must modify them again. If shadromanser can not return the lost limb due to a lack of material, although in case of acute necessity it can spray other parts of the body and create a projection of the lost one. In these cases, shadromancer's face suffers more often. Return the original form of the limb and the lost smoke mass Shadromanser can if only he get a special permission from the one who deprived him of this limb. In the event that the Shadromanser receives a critical amount of damage and can not receive a recover permission, he makes an attempt to rest. He can either be an annihilated Shadromanser-executioner, or lose his emotional component and become a shadow of an object. Being disturbed or attacked, such shadows get mad and attack everything they can get, absorbing and increasing their mass. In this state, they are dangerous and must be destroyed.
Usually such modifications look like "ancient" types - for example, lost hands are changed to big hands, lost ears always became fins, lost leg often became something bird-like. But if damage is more heavy, for example, shadro lost lower part of the body, they can use unusual forms, like octopus tentacles or other things which they count attractive.
Despite the fact, that shadromancers are "smoke mass" of materia units with a core spark at the middle, they prefere to have at least one stable appearance. However, some of them have one or two extra appearances to live calmer.
Where do Shadromancers live? 
Fresh created Shadromancers live in different worlds with their hosts. After they all return to Shado. At the origin Shado is black empty lands with strange black plants and dark grey sky, if it possible to name it so. Sky is always crossed with white stitches, named cuts or maims. Somewhere at the middle of these empty lands DUAU brothers and NN created Shado-city, which gave ability to live like common humans to all shadro, who came to this place. Shado-city is bordered by the high wall, which makes it look like huge bagel, if you will look at it outdoors. Wall is need to protect сitizens from bit-thing-beasts.
How long do they live? 
At the beginning Shadromancers were immortal creatures.
Usually in this process shadromancer starts to personify everything that host (person, who summoned him) does not recognize in himself, or captures the characteristics desired by the host. With this way first summoned shadromancers became very attached to their hosts, and due to it Shado started to produce new core sparks only if someone in random world need it. So, new generations of shadromancers started to depend on hosts and was able to be only CREATED and became partially mortal.
Such shadromancers fully depend on their host's will and have 3 variants of the end of their lifespan:
 became unnesessary to host and being erased (killed) by him
 disappear (die) at the same day as the host
 get a host's last will, which allows shadromancer to live forever, if he will keep safe amount of materia
Can Shadromancers reproduce by they own? 
With a strong suppression of the host and the presence of more than one shadromanser, Shadromancers can be produced in a natural way, but this directly depends on the state and desire of the submissive type. Such children lives not too long, if they won't find ward-dreamer as approval of existense for themselves.
Also if dreamer dies in Shado, or his body died in his birth-world, when soul is in Shado, someone from shadro, usually dreamer's guide, could ask consul and revive dead dreamer into a shadromancer. Usually such "non-core" or "revived" shadromancers have human traits and are similar to human at all. Some of them could get horns or other traits due to shadromancer's physiology.
Also some of dead dreamers could be concluded into mechanical body. But if in first variant dreamer could save his memories, in this variant he loses them and becomes kinda "vegetable".
Can they meet other species? 
Of course. Their hosts or ward-dreamers can be any species from any world. Even feral species, but remember, that host/ward-dreamer MUST have logical mind and MUST able to speak.
Can Shadromancers be in a relationship? 
Yes. But however, shadromancers cannot feel real love, only affection and feeling that he adores to care about someone more than about someone other.
Also romantical relationships between shadromancers and dreamers are strictly prohibited, 'cause if dreamer will die rapidly and won't reach Shado before death moment, HE WON'T BE ABLE TO BE REVIVED AS SHADRO. It will cause huge pain to shadro, affected by him, and such shadro even will wish death to himself. But storyline of Shado remembers some "hybrids" from such "lovestories". "Hybrids" are more likely to be humans with shadromancer's anatomy, they depends on sleeping, are more sensitive and usually have abilities to use artifacts. But also they have to hide their origin, (now) you know why..