svartalfer are not made for the universe as it is now. they are made of what has universally become known as dark matter and are not carbon-based creatures. light and matter are poisonous to them and their suits and masks help slow the deterioration. The more the current universe expands into the dark matter the more they become poisoned; the weaker they become.
while not hivemind, Svartalfer have a connected consciousness to one another that aids in their ability to work, move, and do things harmoniously.
they can be harmed and they can die, but naturally their lifespan is so long that none of them have yet died of old age and it's undetermined whether or not they have an end of life stage or not.
their blood is this weird black substance that kind of evaporates and disappears but the inside of the skin someone sees is also black until the skin repairs.
they do not sweat or produce any bodily odor, they do not need to eat or drink and they need much less sleep than many other species however they can go into a "deep sleep" when needing to reserve energy and pass long periods of time during travel or other issues
they cannot be detected by heat mapping or general senses that would determine whether something is or isn't there. They can be heard, however, if someone has keen ears.
Svartalfar are dignified, proud, eloquent and graceful beings. their forms of intimacy greatly differ from those of humans. pressing your forehead against another's and gripping behind their neck is considered an intense form of respect and intimacy. The harder your push and stronger your grip the greater love and respect lay behind it.
They have varied sexualities just like humans and other species, however their copulation and marriage rituals differ slightly. Sex with any fae-type creature is far more magical in nature. Superficially, sex is the same as humans with the same body parts and so forth, the experience itself is intense and can be overwhelming to those who don't normally experience it. Not only magical but it connects mind, body, and soul.
In contrast to sexuality the Svartalfer are mostly gender-neutral in appearance especially when masked and suited up. Some look more masculine or feminine but more neutral and/or androgynous appearances are really not uncommon. Their language also has only one word that encompasses all identifying genders and this is vath/ovath.
Malekith is the only of his kind who can create life from nothing, as he was created from nothing, as he had to create from nothing to birth his kind. Children are not carried in a womb, they are created then and thereby any two or more elves through mating. The birth of an elf is again more magical than biological. Svartalfer can engage with other species but then cannot create offspring with any species but their own.
dark elves have long since become villainous among the known universe due to their drive to return the darkness, "born of eternal night, the Dark Elves come to steal away the light." Now, most are soldiers, pilots, and engineers. However, long ago they were more commonly scholars and scientists. beautiful and peaceful creatures that knew no war among one another.