Tieflings

It is thought that the horned humanoids known in Yyrda as Tieflings came about through secret dealings with the devils of the infernal plane. Nearly every known human people group in the history of Yyrda has contained a tiefling minority, with some parents giving birth to a child with infernal features for no discernible cause, while others finding themselves transformed after a transaction with a mysterious stranger; still others appear to pass on this heritage through their blood, with a child with one or more tiefling parents more likely than not to possess similar features.
  Due to their infernal legacy, many cultures shun tieflings as cursed and even akin to devils, although the generally xenophobic Falinorian society oddly welcomes tieflings with begrudging respect, likely due to their traditional place among some of the most powerful members of the Arcaneum past and present (including the order’s founder). In other realms such as the Morgani Lowlands, tieflings are generally treated no differently than any of its other diverse peoples.
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Tieflings are notably more common and highly revered in Volskaria throughout its history.

There are a few tieflings with ancestry other than human outside of interspecies reproduction, although a few rare elven tieflings are known to have independently existed in the past.

Although it is not common knowledge, many tieflings do appear to have an innate connection to magic that originates from the infernal plane; particularly strong connections are often associated with a specific archdevil, including Zariel, Mephistopheles, and Asmodeus, with some affected tieflings embracing this connection, and others repudiating it.