Shapechanger. The yuan-ti can use its action to polymorph into a Medium snake, or back into its true form. Its statistics are the same in each form. Any equipment it is wearing or carrying isn’t transformed. It doesn’t change form if it dies.

Innate Spellcasting (Yuan-ti Form Only). The yuan-ti’s innate spellcasting ability is Charisma (spell save DC 14). The yuan-ti can innately cast the following spells, requiring no material components:

At will: animal friendship (snakes only)

3/day: suggestion

Jungle Strider. Moving through nonmagical difficult jungle terrain doesn't cost the yuan-ti extra movement.

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

Slay Foe (1/Turn). The yuan-ti deals an extra 13 (3d8) damage with its weapon attack if it hits a creature that doesn't have all its hit points.

Spellcasting. The yuan-ti is a 9th-level spellcaster. Its spellcasting ability is Wisdom (spell save DC 13). It has the following ranger spells prepared:

1st level (4 slots): ensnaring strike, hunter's mark

2nd level (3 slots): cordon of arrows, spike growth

3rd level (2 slots): conjure barrage, lightning arrow

Multiattack (Yuan-Ti Form Only). The yuan-ti makes two ranged attacks or two melee attacks, but can can constrict only once.

Bite (Snake Form Only). Melee Weapon Attack: +7 to hit, reach 5 ft., one creature. Hit: 6 (1d4 + 4) piercing damage plus 7 (2d6) poison damage.

Constrict. Melee Weapon Attack: +6 to hit, reach 10 ft., one target Hit: 10 (2d6 + 3) 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

Scimitar (Yuan-ti Form Only). Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 7 (1d6 + 4) slashing damage.

Longbow (Yuan-Ti Form Only). Ranged Weapon Attack: +7 to hit, range 150/600 ft., one target. Hit: 8 (1d8 + 4) piercing damage plus 7 (2d6) poison damage.