Tieflings are the recipients of a fiendish legacy that leaves its stamp on them, granting them supernatural gifts.
Tiefling Traits
Creature Type: Humanoid
Size: Medium or Small, chosen when you select this species
Speed: 30 feet
As a Tiefling, you have these special traits.
Darkvision
You have Darkvision with a range of 60 feet.
Fiendish Legacy
Choose a legacy; you gain its level 1 benefit, and higher-level spells at character levels 3 and 5 (always prepared, castable once for free per Long Rest). Intelligence, Wisdom, or Charisma is your spellcasting ability (chosen with the legacy).
Abyssal: Resistance to Poison damage; you know Poison Spray. (3rd: Ray of Sickness; 5th: Hold Person)
Chthonic: Resistance to Necrotic damage; you know Chill Touch. (3rd: False Life; 5th: Ray of Enfeeblement)
Infernal: Resistance to Fire damage; you know Fire Bolt. (3rd: Hellish Rebuke; 5th: Darkness)
Otherworldly Presence
You know the Thaumaturgy cantrip, cast with the same spellcasting ability as your Fiendish Legacy trait.
Source: SRD 5.2.1 · CC-BY-4.0