Members of various races before and after turning into Tirrdaka, by DM.
When any member of any race gets too much exposure to Shadow-Ena when they don't have an affinity towards it, they risk becoming a Tirrdaka. Tirrdaka are basically people who had their body and souls "corrupted" by Shadow-Ena, often resulting in them taking on a very differently looking form; which is the origin of their name, as "Tirrdaka" means, in ancient Vi'hai, "Touched by Darkness". This "corruption" leaves the original personality intact, and the changes are comparatively superficial, like the slight morphing of facial features, development of black sclerae, and the growing of horns and darkly-colored, sharp fangs... even if it does physically alter the composition of ones' soul. Similar to Tieflings, who they're often compared to, Tirrdaka are often misunderstood, but if you make friends with one, you often have a friend for life. The presence of Shadow-Ena in their body and souls also results in an INSANE potential to interbreed; Tirrdaka can have children with nearly every sapient species, which often can result in a Half-Tirrdaka, but sometimes also in another unique type of Tirrdaka, and only extremely rarely in the non-tirrdakan parent's race. Nowadays, Tirrdaka have a unique cultural identity, shaped by Sancstoryl.
A people drenched in darkness
During the so-called Age of Shadows, when Sh'ther Kei-Sihr, the Illiadian deity of shadows, was still known simply as "The Shadow", people tainted by its dark energies became mindless monsters. But then, Rencal Kei-Rhai absorbed it into himself to end its rampage, which in turn stabilized the shadowy energies that were unleashed, and these proto-Tirrdaka regained their minds, becoming the first true Tirrdaka. Nowadays, as previously mentioned, anyone with too much exposure to Shadow-Ena without developing any resistances runs risk of becoming a Tirrdaka.
This corruption by shadow-ena is generally not minded much back on Illiad, where it is seen as a bit of a medical incident, but not much more. However, people from other worlds not well-versed in all things Illiadian sometimes equate this taint and the resulting transformations as a form of fiendish possession or ancestry; which is why, in many areas of the world where Illiadians aren't well-known, Tirrdaka and Half-Tirrdaka are sometimes falsely equated with Tieflings. Worth noting is though, that Tirrdaka, due to their inherent connection to the shadows, are at risk of becoming Feda-Lide after death, which is something that many Tirrdaka fear.
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Racial Traits
Ability Scores: Full Tirrdaka: +1 WIS +2 CHA
Age: Tirrdaka age at about the same rate as humans until they're 21 years old. After this, they'll stop aging physically besides via magical means, and can live up to 500 years old (or 700 if of elven ancestry), should they succumb to Ha'zas Syndrome. If they don't die from it, they can't die of old age anymore, effectively making them capable of living forever.
Alignment: Due to their exposure to Shadow-Ena, Tirrdaka and Half-Tirrdaka tend to lean slightly towards chaotic alignments, even though lawful Tirrdaka are definitely not unheard of.
Size: Medium or Small
Speed: Walking: 30ft
Languages: Common, Standard Illiadian or Draconic Illiadian (or another language that fits you)
Specks of Obsidian: Your soul and body are tainted by Shadow-Ena, giving you resistance to Shadow-Ena, overriding any conflicting vulnerabilities. You also have a natural immunity towards corruptive shadow-ena effects that could turn you into a Tirrdaka (if you're a Half-Tirrdaka), Light-Walker or Shadow-Walker. You also gain the trait Heart of Illiad, with your Ena-type chosen by you. It can not be "Heart of Obsidian".
Darkvision: Your vision can easily cut through darkness. You can see in dim light within 60 feet of you as if it were bright light, and in darkness as if it were dim light. You can't discern color in darkness, only shades of gray.
Tirrdaka Origin Feature (choose two): You may chose a feature from another race, which you either were before becoming a Tirrdaka, or is the origin of your Tirrdaka bloodline. Your physical appearance is based on the race that this feature is from. This feature can be a type of movement (flight, swim speed etc.).
Feda-Lide Risk (Full Tirrdaka): When you die in combat by failing your death saves or by being killed instantly, roll a D20. If you roll a natural 20, you come back as a Feda-Lide with 50% of your health, rounded down. This is true, even if you're killed by Finger of Death, but not by Disintigrate. After this, roll a D100, as there's also a 50% chance of said Feda-Lide version becoming a mindless Type Alpha Feda-Lide that attacks any creatures around it indiscriminately to feed on their souls. If you roll a 50 or below on your percentile dice, you permanently relinquish control of your character to the DM. This can only be reversed by killing the Feral Feda-Lide version of yourself and casting Revivify, Raise Dead, and other resurrection-spells on you within 24 hours, turning you back into a Tirrdaka. Reincarnate will also not turn you into anything but a Tirrdaka for this purpose. If you're resurrected after 24 hours, you don't turn back into a Tirrdaka, but rather another Feda-Lide, but this time, the chance of you becoming a Type Alpha drops to 25%.
If you roll above 50%, you become a Type Gamma Feda-Lide or, at your DMs digression, a Type Beta. Until you have consumed your first soul, control of your character is only temporarily relinquished to the DM due to you becoming hunger-crazed. The crazed Feda-Lide version of you nonetheless can recognize friend and foe and is unlikely to attack close friends, unless it is desperate to feed and senses no other food sources. After consuming its first soul, as by the Feda-Lide feature "Soul Food", control of the now Feda-Lide is relinquished back to the player and you are incapacitated for 1 hour and unconscious, but are at full HP and can only remember any events from your hunger-craze in a dreamlike haze.
--- Illiadian Trait (Only works on Sancstoryl, Illiad, or if two other Ena-Users are within 300ft from you ---
Ena Mastery: You still have access to the lost art of Ena and can use Ena-Techniques worth up to 3 Ena-Points after each short or long rest. You gain two additional points at Level 4, 8, 12 and 16, and three at Level 19. Your Ena-ability is either Charisma, Intelligence or Wisdom and chosen by you.