Innate Spellcasting (Yuan-Ti Form Only). The yuan-ti's innate spellcasting ability is Charisma (spell save DC 13). The Yuan-Ti can innately cast the following spells, requiring no material components.
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 its wearing or carrying isn't transformed. It doesn't change form if it dies. Magic Resistance. The Yuan-Ti has advantage on saving throws against spells and other magical effects.
Multiattack (Yuan-Ti Form Only). The Yuan-Ti makes two ranged attacks or two melee attacks, but can use its bite only once. Bite. Melee Weapon Attack. +5 to hit, reach 5ft, one creature. Hit: 5 1d4+3 piercing damage plus 7 2d6 poison damage. Scimitar (Yuan-Ti Form Only). Melee Weapon Attack. +5 to hit, reach 5ft, one target. Hit: 6 1d6+3 slashing damage. Longbow (Yuan-Ti Form Only). Ranged Weapon Attack. +4 to hit, range 150/600ft, one target. Hit: 6 1d8+2 piercing damage plus 7 2d6 poison damage.