Elavi

It took me a while, I know, I know... 

However, not because I'm lazy - I mean, don't get me wrong, I am lazy, but I had a different reason. I effectively forced myself to draw this one, sort of as a head start. I still have three weeks of HCV therapy left and I feel quite terrible.
Despite relative simplicity of this drawing, it took me a while to finish, and I'm not counting figuring out the design, just the drawing itself. Still, I didn't loose my form, not completely anyway.

In any case... Lore time!

"Why don't you let me make your dream come true? I could become that dream."

They call themselves Elavi, though most call them changelings, shapeshifters or mimics. They are one of many alien species of my universe and are one of the most unique.

Elavi, in their natural form are slightly shorter than average human, but comparatively heavier and are gifted with strange, elusive beauty and grace. Their bodies are adorned with sets of tape-like tentacles creating a form of a natural outfit.  Their bodies are soft and appear to be rather fragile, though this flaw is mitigated by their incredible regenerative capabilities. 
Their bodies share similar proportions to these of a humans, through their hips are incredibly wide, as they act as storage for nutrients required for both regeneration and shapeshifting.
They have two sets of eyes - small ones for the day and large ones, capable of night vision. Due to their sensitivity to light, the large eyes remain closed most of the time, giving the Elavi rather strange, always stoic appearance - they appear as if they were sleeping or meditating most of the time.
Most of their senses are not very acute, however, with the sole exception of touch. Members of this species communicate with each other mostly through direct contact. They are also psychics specialized in touch-based telepathy, which they use to share memories and experiences with one another, making them incredibly fast learners.

Probably the most amazing ability of that species is shapeshifting - they are able to absorb tissues of other species and instinctively analyse their genetic material to later force own body to recreate it. Elavi are able to completely change their shape and perfectly mimic any other species of similar size after few days of regular, direct contacts. Transformation, however, is a slow, and energy consuming process - depending on specimen and complexity of mimicked organism, it may take anywhere between 8 and 48 hours. However, the copy is almost perfect. Elavi tend not to transform fully unless it is absolutely necessary - they usually just copy single organs that are convenient to them, like voice cords, as they are naturally mute. 
In addition, their touch-based telepathy allows them to quickly learn behaviour of mimicked species in most cases. 
Transformation and morphing additional organs are fully conscious actions and each Elavi has direct control over what is morphed and when. They also do not forget the genetic material once absorbed and the ability to transform can be perfected as any other skill. On a baseline, instinctive level, Elavi can simply copy full form or specific body parts. With more training, the copies may be perfected, for example to mimic not only the species, but also a specific person - down to every physical detail. In time, many Elavi also learn to modify and fine tune the genes they absorbed, forcing morphed organs and body parts to work and look as if they were natural parts of their bodies in the first place, creating a seamless blend. Many Elavi get fine tune their bodies to such a level in a pursuit after ultimate beauty and self-discovery that they become living works of art. 
However, reckless morphing can lead to some undesirable consequences, and some Elavi become lost in it, turning themselves into de-facto monsters with little to no chance of return to norm. 

Elavi's regenerative abilities make them biologically immortal.

Elavi are genderless species - they exchange their genetic material casually through touch. After the exchange is complete, they both lay eggs. They can also reproduce asexually, effectively creating clones of themselves. 
Despite that, they often create very long term relationships with one another and they do not mind interspecies contacts - which is easy for them due to their shapeshifting abilities.

Elavi society appears very strange to the outsiders - it is very private, unusually peaceful and intimate as they require touch to communicate fully. However, this also means that they are very compassionate and understanding creatures, often almost unnaturally charismatic and helpful. They are natural-born diplomats, and passionate lovers that do not see the problems of interspecies contacts. They do not wear any clothes, as they would interfere with their tentacles.

Elavi are currently members of an ancient alliance of three alien species, known as The Tribunal. It is an ancient union of very old species that faced and won against the very first Ancient Plague (to them known as the Great Plague). 
During the outbreak of the Great Plague, Elavi were on the very front line, the Plague has seen their adaptive abilities as a major threat and attacked with full force. Elavi homeworld was nearly completely destroyed and the species itself took heavy losses, but was crucial in stopping the Plague. The beast was unable to absorb them, which gave them a massive advantage in conflict.
Currently, Elavi do not have their own worlds - they tend to live among other species of The Tribunal, sometimes in small communities, sometimes blending in a society. 
They are generally seen as compassionate souls, solving conflicts in a peaceful manner and are generally admired for their gentle way of living. 
When it comes to technological level - Elavi excel at medical technologies. Their natural abilities to analyse genetic material allowed them to develop some extremely effective methods of treatment. They are no warriors, though some Elavi made great careers in intelligence.