Shadar-kai

Ow the edge.

Even more edge.

Shadar-kai are a Dungeons & Dragons creature where you really have to specify what edition you're talking about. Both versions have a gothy sadomasochistic theme (imagine a whole race of Cenobites from Hellraiser), but the difference between 3e and 4e really couldn't be much greater.

In 3rd Edition

An obscure beastie, the 3.5 shadar-kai is a species of Fae that has been dwelling on the Plane of Shadow for generations. This has caused them to suffer a magical affliction where they steadily fade away into nothingness, unless they can stimulate themselves. The most easy way to do this is via torture and self-mutilation, to the point that their iconic gear are arm-bands with cold iron spikes on the inside, which they drive into their own flesh to keep them "anchored" into reality. They hate all mortals for not having to put up with the same effect, blaming them for their choice to live in the Plane of Shadow in the first place.

In 4th Edition

Debuting in Dragon Magazine #372, the shadar-kai of the World Axis became both a humanoid race and a playable species. Basically, they're the descendants of humans who migrated to the Shadowfell in pursuit of immortality. They got it... of a sort. If they can keep themselves active, amused and interested in life, they can live forever. If they succumb to ennui, they start fading out of existence. Their culture is thusly dedicated to stimulation of all sorts: carnal experimentation and sadomasochism, boasting contests, athletic contests... in essence, they're a race of "live for the moment" loudmouthed jocks, with a tendency to cut themselves when things get boring.

Ability Scores: +2 Dexterity; +2 Intelligence or +2 Wisdom (originally, they were a Dex/Int race, with Dragon #397 letting them trade the Int for a Wis bonus instead.

Size: Medium

Speed: 6 Squares

Vision: Low-light

Languages: Common, one language of choice

Skill Bonuses: +2 Acrobatics, +2 Stealth

Shadow Jaunt: Once per encounter, as a move action, teleport 3 squares and become Insubstantial until the start of your next turn.

Shadow Origin: Considered a shadow creature for the purpose of effects that relate to creature origin

Winterkin: +1 racial bonus to Fortitude defense, +2 racial bonus to death/unconscious saving throws

In Dragon Magazine #391, the article "A Legacy in Shadow" officially canonized/examined the presence of shadar-kai in the Forgotten Realms, saying they began to spontaneously arise as a result of the Spellplague touching the shadowborn humans brought back to Toril by the Shadovar of Returned Netheril. This not only provided a number of new racial feats, but also included the subraces/alternative powers for shadar-kai descended from shades and krinth, represented as a pair of Heritage Feats:

• Krinth Heritage: +2 to Intimidate, become Insubstantial until the end of your next turn when you suffer a critical hit from an enemy, replace Shadow Jaunt with Demonic Aggression (1/encounter, as an immediate reaction to being damaged by an enemy within 3 squares, teleport to an unoccupied square adjacent to that enemy and gain combat advantage until the end of your next turn).
• Shade Heritage: Vision becomes Darkvision 5, +2 to Stealth checks (so +4 total), replace Shadow Jaunt with Shade Stride (1/encounter, teleport either to any square within 5 squares or to any dark or dimly lit square within 10 squares as a move action).

In 5th Edition

Shadar-kai made an appearance for 5e in the November 2017 issue of Unearthed Arcana; whilst the focus was purely on crunch, their fluff was essentially a clumsy amalgamation of their lore from before - in a nutshell, taking all of their 4e lore, but making their base race be elf rather than human. As such, they are mechanically a subrace for elves, although their entire statblock is repeated here because 1d4chan is awesome like that.

Ability Score Increase: +2 Dexterity, +1 Charisma

Size: Medium

Speed: 30 feet

Darkvision 60 feet

Keen Senses: Proficiency in Perception.

Fey Ancestry: Advantage on saves against being charmed, and immune to magic that puts you to sleep.

Trance: Trancing for 4 hours yields the same effect as an 8 hour sleep.

Deathly Cantrip: You know a single cantrip chosen from a list of Chill Touch, Spare the Dying and Thaumaturgy. This cantrip can't be changed at a later date. Your spellcasting ability score for this cantrip is Charisma.

Blessed By The Raven Queen: You can use a bonus action to teleport to an unoccupied space within 15 feet. After teleporting, you gain resistance to all damage until the end of your next turn, during which time you appear translucent and ghostly. After using this ability, you must complete a short rest or a long rest to use it again.

Shadar-kai later appeared in Mordenkainen's Tome of Foes but with some edits. The most notable among these changes includes the Deathly Cantrip being removed but the range of their teleport is increased to 30 feet. A new interesting detail for them is that they look like actual wrinkly old people while they're in the Shadowfell for some reason. Also, they're no longer BDSM freaks, instead they just treat their bodies as disposable since they know their Raven Queen will resurrect them anyway.

Mordekainen's Monsters of the Multiverse saw another edit, splitting them off from the general Elf race like the Eladrin. This rewrite makes their stat increases fall into lines with the current paradigm of pick-your own stats (+2/+1 to two stats or +1 to three) and providing multiple uses of their teleport power equal to their proficiency bonus, but ultimately little else.

Ability Score Increase: +2 Dexterity, +1 Constitution

Size: Medium

Speed: 30 feet

Darkvision 60 feet

Keen Senses: Proficiency in Perception.

Fey Ancestry: Advantage on saves against being charmed, and immune to magic that puts you to sleep.

Trance: Trancing for 4 hours yields the same effect as an 8 hour sleep.

Necrotic Resistance: You have resistance to necrotic damage.

Blessing of the Raven Queen: You can use a bonus action to magically teleport to an unoccupied space you can see within 30 feet. Starting at the 3rd character level, you gain resistance to all damage after teleporting with this trait until the start of your next turn, during which time you appear translucent and ghostly. After using this ability, you must complete a long rest to use it again.

If you want something closer to the 4e version of the race, Ulraunt's Guide to the Planes has got you covered!

Ability Score Increase: +2 Dexterity, +1 to an ability score of your choice

Size: Medium

Speed: 30 feet

Darkvision 60 feet

Shadow Blend: While in dim light or darkness, you can use a bonus action to become invisible, along with anything you are wearing or carrying. The invisibility lasts for 1 minute, until you make an attack or cast a spell, are in bright light, become incapacitated, or until you use a bonus action to end it. Once you use this trait, you can’t use it again until you finish a long rest.

Shadow Jaunt: When you are in dim light or darkness, as a bonus action you can teleport up to 60 feet to an unoccupied space you can see that is also in dim light or darkness. Once you use this trait, you can’t use it again until you finish a short or long rest.

Shadow Stealth: While in dim light or darkness, you can take the Hide action as a bonus action.

Spiked Chain Proficiency: You are proficient with the spiked chain and the heavy spiked chain.

Languages: You can speak, read, and write Common.

Epic Racial: Ghostly Jaunt: When you reach 25th character level, after using your Shadow Jaunt, you gain resistance to all damage until the start of your next turn.