Yuan-Ti

Size. You are Medium or Small. You choose the size when you select this race.

Darkvision. You can see in dim light within 60 feet of you as if it were bright light and in darkness as if it were dim light. You discern colors in that darkness only as shades of gray.

Magic Resistance. You have advantage on saving throws against spells.

Poison Resilience. You have advantage on saving throws you make to avoid or end the poisoned condition on yourself. You also have resistance to poison damage.

Serpentine Spellcasting. You know the poison spray cantrip. You can cast animal friendship an unlimited number of times with this trait, but you can target only snakes with it. Starting at 3rd level, you can also cast suggestion with this trait. Once you cast it, you can't do so again until you finish a long rest. You can also cast it using any spell slots you have of 2nd level or higher.

Intelligence, Wisdom, or Charisma is your spellcasting ability for these spells when you cast them with this trait (choose when you select this race).

Languages. You can speak, read, and write Common and one other language that you and your DM agree is appropriate for your character.

Source: MPMM, page 36

Yuan-ti were originally humans who transformed themselves into serpent folk through ancient rituals. Most yuan-ti were corrupted into monsters by those rites, but some yuan-ti instead became a new people who mix characteristics of humans and snakes.

Blessed with resistance to magical and poisonous effects by the rituals that created them, each of these yuan-ti manifests their serpentine heritage in a variety of ways: a forked tongue, snake eyes, a snakelike nose, or some other ophidian characteristic. However a yuan-ti looks, they have the power to pursue great good or evil in the multiverse.