PHB, Homebrew, MotM
Tieflings outside the Acapellago are rare. After several deals were being made in Dixieland, though, they are a more common sight in the island chain. Many tieflings end up orphans for one reason or another. Those who do grow up with at least one parent, often the human parent, may be a bit more accepted by their local town. Overall, tieflings learn a significant modicum of self-reliance early in life and are slow to trust others.
If playing with achievements and milestones, choosing this race at character creation grants the player the achivement "Devil in Me."
Darkvision. Thanks to your infernal heritage, you have superior vision in dark and dim conditions. You can see in dim light within 60 feet as if it were bright light, and in darkness as if it were dim light. You can't discern color in darkness, only shades of gray.
Hellish Resistance. You have resistance to fire damage.
Infernal Legacy. You know the thaumaturgy cantrip. When you reach 3rd level, you can cast the hellish rebuke spell as a 2nd-level spell once with this trait and regain the ability to do so after you finish a long rest. When you reach 5th level, you can cast the darkness spell once with this trait and regain the ability to do so when you finish a long rest. Charisma is your spellcasting ability for these spells.