Shapechanger. The yuan-ti can use its action to polymorph into a Large 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.

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

Magic Weapon. The yuan-ti's weapon attacks are magical.

Multiattack ( Ignan Form Only). The yuan-ti makes four attacks: two with its mace, one with its gore, and one with its tail slap

Mace. Melee Weapon Attack: +8 to hit, reach 5 ft., one creature. Hit: 12 (2d6 + 5) bludgeoning damage plus 3 (1d6) fire damage.

Gore. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 9 (1d8 + 5) piercing damage.

Tail Slap. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 10 (1d10 + 5) bludgeoning damage, plus 3 (1d6) fire damage. and if the target is Large or smaller the target is grappled (escape DC 16). Until this grapple ends, the target is restrained, and the yuan-ti can’t tail slap another target. and the target takes 15 (3d6 + 5) bludgeoning damage plus 7 (2d6) fire damage.