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The tieflings are a race of humans with the taint of demonic blood. Tieflings appear human except that they exhibit at least one demonic trait, usually horns, a forked tongue, smoldering pupil-less eyes or a tail. The tieflings are usually referred to as the Spawn of Azreal, as over the last two hundred years, Azreal has mated with hundreds of mortal women in a search for the “perfect” mortal child. Most tieflings band together to form cults to their Demon Father, but many go into hiding within society, trying to escape their abyssal heritage.
Tieflings follow the rules in the PHB except anything referring to “infernal” is instead “abyssal” as they have demonic and not diabolic heritage. They are permitted to take Abyssal as a starting language.