Shapechanger. The yuan-ti can use her action to polymorph into a Large snake, or back into her true form. Her statistics are the same in each form. Any equipment she is wearing or carrying isn’t transformed. She doesn’t change form if she dies.

Magic Resistance. The yuan-ti has advantage on saving throws against spells and other magical effects.

Divine Eminence. As a bonus action, the yuan-ti can expend a spell slot to cause her melee weapon attacks to magically deal an extra 10 (3d6) radiant damage to a target on a hit. This benefit lasts until the end of the turn. If the yuan-ti expends a spell slot of 2nd level or higher, the extra damage increases by 1d6 for each level above 1st.

Spellcasting (Abomination Form Only). The yuan-ti is a 9th-level spellcaster. Her spellcasting ability is Wisdom (spell save DC 13, +5 to hit with spell attacks). The yuan-ti has the following cleric spells prepared:

Cantrips (at will): light, sacred flame, thaumaturgy

1st level (4 slots): cure wounds, guiding bolt, sanctuary

2nd level (3 slots): lesser restoration, spiritual weapon

3rd level (2 slots): dispel magic, spirit guardians

Innate Spellcasting (Abomination Form Only). The yuan-ti's innate spellcasting ability is Charisma (spell save DC 16). The yuan-ti can innately cast the following spells, requiring no material components:

At will: animal friendship (snakes only)

3/day: suggestion

1/day: fear

Multiattack (Abomination Form Only). The yuan-ti makes two ranged attacks or three melee attacks, but can use her bite and constrict attacks only once each.

Scimitar (Abomination Form Only). Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 12 (2d6 + 5) slashing damage.

Constrict. Melee Weapon Attack: +9 to hit, reach 10 ft., one target Hit: 12 (2d6 + 5) bludgeoning damage, and the target is grappled (escape DC 16). Until this grapple ends, the target is restrained, and the yuan-ti can't constrict another target

Bite. Melee Weapon Attack: +9 to hit, reach 5 ft., one creature. Hit: 8 (1d6 + 5) piercing damage plus 10 (3d6) poison damage.

Snake Antipathy (Abomination Form Only; Recharge 6). The yuan-ti targets a creature she can see within 60 feet of her. The target must succeed on a Wisdom saving throw or feel an intense urge to avoid snakes and snakelike creatures (including yuan-ti), as if affected by the antipathy effect of an antipathy/sympathy spell. The save DC is the same as that of the yuan-ti's Innate Spellcasting ability.

Smite (1/Turn). As a bonus action, when the yuan-ti hits a creature with a weapon attack, she can expend a 1st level spell slot to deal 2d8 radiant or necrotic damage to the target. If the yuan-ti expends a spell slot of 2nd level or higher, the extra damage increases by 1d8 for each level above 1st (maximum 5d8).