Tieflings are a half-race in Quelmar, affected with demonic or infernal blood, brought onto their family typically through a deal with a devil, or the curse of a demon.
About
Some tieflings are born displaying their fiendish heritage outright, while others, especially newly affected bloodlines, may appear normal at birth, and slowly reveal their infection over time.
It is possible to suppress a tiefling's cursed appearance and powers at birth through holy ritual, though the upkeep of said rituals becomes harder over time, and the more the suppressed creature exerts themselves (especially if their Tiefling heritage includes any magical powers), the more likely they will expose their truth.