Tiefling

There are two types of Tieflings in Edda. First are those who were created when Mana became Flesh in the wake of The Second Cataclysm. The Mana clumps that had been laced within smooth, lustrous gems and their connected stone found themselves with skin of many colors, just like the gems they had inhabited, and elegant horns as well. These are colloquially known as The Gemborne.
The second type is those who find themselves with Demonic Blood flowing through their veins, creatures born from vitriolic emotions of many kinds, the emotional energy springing to life in The Triad of Hell. These are Infernal Tieflings.
Functionally, the two are nigh-indistinguishable, save for a few differences: Gemborne have smooth horns, and typically look more like regular mortals. Infernal Tieflings, on the other hand, typically have slightly ribbed horns, much like goats or rams, and tend to have more uncommon body features, such as cloven hooves for feet, tails, or wings.
Either way, the two types share much in common, most notably their ability to channel natural mana within themselves for a wide variety of effects. This depends on their background and where their power springs from, but it's always an adept control of their internal power.

Naming Traditions

Unisex names

Most of the naming conventions within Tiefling families depend on the region they stem from, but long-lasting families will usually have names based on the gemstones they originated from or adjectives related to them. A unique feature among Infernal Tieflings that has spread to Gemborne is the ideal of Virtue Names, meaning a name that one chooses for themselves throughout their life to represent their ideals, core beliefs, or other important parts of their personality.

Culture

Major language groups and dialects

Tieflings in the modern-day mostly speak Infernal, a language that's a cross between the Gemborne language and the native Infernal Tiefling language of Abyssal, although some Infernal Tieflings speak it natively as well.

Culture and cultural heritage

The culture of a Tiefling, or a Tiefling family, will be largely loose and freeform. Don't expect to find many family heirlooms or generational artifacts, as each member in a family will have items they uniquely hold dear. It isn't too uncommon to find Tiefling children who grew to appreciate the aesthetics they were raised around, but it isn't common.

Shared customary codes and values

The ideal that's passed down the generations by Tiefling households is Individuality. Personal expression, personal aesthetic, personal confidence, personal education, it's all very important that each Tiefling be the best person according to themselves, rather than trying to be like someone or something else to appease them.

Common Etiquette rules

While Gemborne Tieflings generally follow the traditions of the area they were raised in, Infernal Tieflings have a much different sense of things, due to their generational customs coming from the Hells. The most common etiquette among Infernal Tieflings is to never directly ask if someone desires something. In the plane of deals and trickery, it's considered most polite to allow the guest to request something, and then comply, although asking clarifying questions isn't deemed impolite, as the casual nature of the request has already been declared.

Common Dress code

Tieflings will wear the most glamorous, pricy, ostentatious clothing, or the cheapest, dirtiest, most disheveled clothing as long as it fits their personal aesthetic. But, the constant is how drastically they go on the spectrum. To put it in layman's terms, Tieflings have 100% No Chill about their fashion sense.

Art & Architecture

Gemborne Tieflings in the past have reflected their generational sense of extravagance and individuality by focusing heavily on the various arts of the world. Painting and Fashion Design are the two most common among them, but look at the famous names of any type of artistry, and there's a good chance a Tiefling will be in the top 10. 
Infernal Tieflings tend to have a much more focused sense of art and architecture, using dark stones and bricks along with wrought metal in a very brutalist style of architecture, and their generational art is not much different, utilizing dark colors and dramatic shapes.

Common Customs, traditions and rituals

The most common tradition among Tiefling communities is the yearly holiday of Jour de Glamour, on the 10th day of Melting Winter. Beginning some 100 years ago in Paris, it's a day in which Tieflings gather in droves to show off their most fashionable and glamorous outfits. Full of dancing, merriment, and show-offs, some larger cities have taken it as an opportunity to host Tiefling centered fashion shows or other such events.

Coming of Age Rites

When a Tiefling is seen as an adult, usually between 16-18 years of age, they choose their name, either a changed family name or a Virtue Name.

Funerary and Memorial customs

When a Tiefling passes away, it's customary for their family and friends to come together after their cremation (the typical burial style for Tieflings) and fill their grave with trinkets either from their house, or that they would like, and give a final toast as they are buried underneath the earth.

Ideals

Beauty Ideals

Tieflings prize individuality above all else, so each Tiefling will have their own standards and goals for beauty and fashion along with their own mental images of their aesthetics.

Gender Ideals

Most modern Tieflings won't care too much about the line between masculinity and femininity, as there isn't much dimorphism between the sexes outside of genitalia, and even then there is a large number of Tieflings that could be considered intersex medically, about 1 in every 3,000.

Courtship Ideals

Many having compared the "ideal" courtship between Tieflings to flamboyant birds, as there is a great amount of showmanship, effort, and glamour assigned to the task. However, the strict definition of those terms depends on the aesthetic of the courter and the courted. For example, if a High Fashion courted was given a pristinely decomposed deer skull by a more corvid-core courter, it might not seem to be a match, but the effort and meaningfulness of the gesture, combined with the commitment to one's personal values, would garner a high level of appreciation.

Relationship Ideals

Among Tiefling relationships, both Gemborne and Infernal, there aren't many strict ideals, as all sides of a relationship are intended to do what is necessary for survival and happiness. However, due to the individualistic nature of Tieflings, it's a key component that each side of a relationship does not interfere or tear down the personal growth or expression of another, and instead support and build it up.