To be greeted with stares and whispers, to suffer violence and insult on the street, to see mistrust and fear in every eye: this is the lot of the tiefling. And to twist the knife, tieflings know that this is because a pact struck generations ago infused the essence of Dagon, overlord of the Shadowsea (and many of the other powerful devils serving under him) into their bloodline. Their appearance and their nature are not their fault but the result of an ancient sin, for which they and their children and their children's children will always be held accountable.
Though rare, there are children born to all sentient races with a tiefling nature, proof of an interaction or pact with the Lord of the Shadowsea in the distant past. Ocean-born teifling children tend towards a brilliant/striking coloration regardless of their natural ancestry, reminiscent of poisonous water creatures. Some communities welcome and guard their tiefling children jealously, others cast them out as unlucky or proof of bad blood.