Etymology and definition
Elfs are classified in the 'homo' genus and share common ancestory with other species like Humans and Vedalken. 'Arbor' comes from old human mythos that described elfs as being the decendents from trees and ents. Homo Arbor became a sort of misnomer that stuck to elvish genus as more accurate scientific discovery behind their history was uncovered. Neverthelss Elf was the official name for their species, carried over from the elvish language itself which is used even today.
Biology
Anatomy and Physiology
From a distance, elfs look remarkably like an ordanary human and much of their anatomy and physiology is very similar. The elvish body consists of the legs, torso, arms, neck and head. Their ears are notibly much longer than a human and are pointed rather than rounded. Elfs are usually taller and slimer than humans and may often have longer limbs. Their skin tones are usually fair, though it's not unusual to find an elf with more tanned skin. Elfs have keenly eveloved set of eyes than have adapted to see in much more dimly lit areas. Their larger and pointed ears also give them a much better sense of hearing than many of the other species that inhabit Ravnica.
Elfs also have a developed sensory organ similar to a human's "magical animus." Aptly named "life animus" elfs can detect life around them. The exact distance of this sense depends on the individual. Physical touch can also give an educated elf insight to any ailments the individual may be carrying.
Life Animus
Elfs are capable of innately sensing life in an area around them. How far one can detect life is based on the individual, but it is safe to assume that most elfs are capable of detecting life in no more than 20 meters around them. Anything that can be considered alive falls under their senses. A blade of grass, a person, or even an artifact that has been given life through magical means. An elf can differenciate between the many forms of life. For instance, they can tell what is a tree and what is a being, but being able to accurately pinpoint if the being behind a door is a human, or a dog, is more difficult. Masters of this scent are capable of detecting what species the life form can belong to, and can even tell individuals apart from a crowd.
Due to the nature of life being everywhere, many elfs simply tune this sense out, like tuning out a buzzing noise or adjusting your eyes to a new source of light. More weary elfs may focus on this sense, keeping tabs on all the life around them to make sure they are not being stalked or to make sure that no one can sneak up on them. There are magical means of tricking this sense or bypassing it altogether. Undead creatures cannot be detected, there are spells to mask life from the scent, and individuals may use magic to mimic life or use actual living creatures to cause diversions or confusion to elfs relying too much on this scent. A sufficiently thick material like stone is also capable of muting this sense if not outright denying it altogether.
Life Cycle and Sexuality
Elfs have fully functional sexual organs up until a certain age late in life, usually up until around the age of 250. A female who is impregnated will carry the child for about a year before she will give birth. The elf baby is very vulnerable and must be carefully looked after until the age of about three. Elfs are also capable of interbreeding with other races that fall under their similar genus, though these offspring are almost entirely sterile and cannot breed further. Childen who are born this way will usually carry traits from both their parents; longer ears from an Elf or shorter limbs from a Dwarf, for example.
An elf reaches maturaty much faster than other species, and is considered fully physicaly and mentally developed by the age of 18. The average elf lifespan is around 300, with some elfs living upwards to 400 years and beyond.
Diet
An elf diet can be omnivores, though many choose to become vegetarians or vegans.
History
Elfs throughout recorded history have mostly lived in Ravnica's forests and jungles. These people were very recluse and often refused to take part on much of the world's affairs. Due to their isolationist stance, much of their technology stagnated when compared to human and dwarf ingenuity, and as a result their homes were taken over and destroyed for the ever expanding dominions of the empires and kingdoms. Wars were fought over these transgressions, but few ever succeeded. Most elven people were forced to migrate into the cities they despised, and were subjected to hostile racism and bigotry until much later when they became more integrated into societies.
"Life grows everywhere. My kin merely find those places where it grows strongest."— Nissa Revane
Society and Culture
Elves today have long been fully integrated into society and have not suffered mass bigotry for generations. Elfs are naturally empathetic towards nature, so many will form communities around reclimation zones or areas with a high concentration of natural life. It's still not unusual to come across Elfs who simply live within the urban sprawl, however.
Due to the elf's natural fondness of nature, they almost exclusively follow the tenets of Green Mana. The Selesnya and Golgari are dominated by the elf population, and with a sizable force within the Gruul ranks.
Devkarin Elves
Devkarin are the dark elves of Ravnica. Formerly, they made up one of the two elite classes of the Golgari, the other being the teratogens. They are presided over by their "Matka", a high priestess, who until recently was Savra. The current Matka is Izoni, Thousand-Eyed. The Devkarin are adept spellcasters counting most of the Golgari's shamans among their numbers. Some of the Devkarin wear Moodmarks, which are minor enchantments that appear as spots or markings on their foreheads and around their eyes (usually resembling insect eyes).
Silhana Elves
The Silhana are the Ravnican elves that are part of the Selesnya Conclave. The Silhana are master archers who stalk the rooftops of the city-plane. Some Silhana, the Elves of Deep Shadow, were cast out of the Conclave long ago and joined the Golgari.
Simic Elves
There was once a third tribe of elves on Ravnica, one that became largely extinct during the pre-Guildpact wars; the survivors joined the Simic Combine. Little is known about them, but both the Devkarin and the Silhana believe they were very cruel and unpleasant. Simic elves seem to have been mostly bald. As time went by, almost all of the Simic elves subjected themselves to strange biological experiments, adding biomechanical implants or splicing their genes with those of other creatures, such as snakes.
Gruul Elves
Elves who became fed up with slow progress of Selesnya have taken up arms within the Gruul Clans. They wish to quicken the reclimation of Ravnica by any means necessary, and make up very dangerous squads of geurilla fighters. These fighters are typcially placed deeper within Gruul territory where nature has taken over and employ hit and run tactics against enemies who are less familiar within their favored habitat. These elves specialze in stealth and finesse counter to what most Gruul's more abbrasive tactics.
Underrealm Lich by Anna Steinbauer
A Golgari Elf
Language
Elves posses their own language simply named "Elvish."
Religions
Most elves are very keep to worship
Nylea, God of the Hunt. Undercity elves are noted to worship Pharika, God of Affliction. Karametra, god of Harvests is also a popular deiety among the evlish populations.
Inter-species relations
Friendships and enemies form fairly naturally from each individual, though a person with destructive tendancies towards nature will often be shunned away from an elf, whether the elf does so consciously or not.
"The spires of Ravnica are no different from the tall trees of other planes. The elves navigate and protect them just the same."
I like the concept very much... seems very interesting.