Coal Elves

Often mistaken for drows, the coal elves are in reality more similar to tieflings, though not classified as such. Although not actually elves, coal elves is what they are called by people outside their own kind. They are in fact a type of changeling.
Although changelings, and thus able to change their appearance at will, coal elves in their most basic form have dark skin similar to drows, various shades of purplish ashen in colour, caused by the poisonous air that exists within the Coal Desert. Their hair can be any colour, but it is not uncommon for them to have hair that is of varying tones of red or purple. As the coal desert is a hot, harsh place, the coal elves resistance to fire gives them an edge with surviving in the coal desert. The soles of their feet are hard, allowing them to walk barefoot on the burning hot desert ground, and their vision is slightly decreased because of the constant red brightness emanating from the glow beneath some places under the burnt sand and coal dust.
The coal elves have developed a resistance to poison, as everything around them carries some level of it; even the coal elves themselves. If a creature not immune to poison were to bite a coal elf, that creature would be poisoned. Their poison isn't lethal to creatures of small or larger size, though the poison does cause nausea.
The coal elves are carnivores, and have developed a skill with which to selectively breed creatures to be able to resist the inhospitable area that is the coal desert. Of course, this means making the creatures poisonous to a certain level, as they also build up the creatures' poison resistance.
It is said that they have influences from the abyssal or infernal planes, as it is thought that the glowing pools beneath the coal sand of the vast lava field can be utilized as portals to those planes, and they do have an easy time learning the infernal and abyssal languages. Their names are also influenced by this, making them sound guttural with plenty, if not solely, of consonants.

Subclass Traits

Ability Score Increase. Your Constitution score increases by +2.
Languages. You can speak, read, and write Infernal or Abyssal.
Poisonous. You are considered a poisonous creature, and your blood contains a non-lethal poison. You have advantage against any form of poison damage.
Fire Resistance. You have advantage against fire attacks and the soles of your feet in particular are immune to fire damage. You do not get harmed from moving through firey and particularly hot areas.
Cold Sensitivity. You have little experience with cold climates. In fact, you might considered what others see as normal temperatures as chilly. As such, you don't fare well with particularly cold temperatures and have disadvantage against cold damage.