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.

Innate Spellcasting (Abomination Form Only). The yuan-ti's innate spellcasting ability is Charisma (spell save DC 15). 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

Magic Resistance. The archdruid has advantage on saving throws against spells and other magical effects.

Spellcasting. The archdruid is an 18th-level spellcaster. Its spellcasting ability is wisdom (spell save DC 17, +9 to hit with spell attacks). The archdruid can cast alter self and invisibility at will and has the following druid spells prepared:

Cantrips (at will): druidcraft, guidance, poison spray, resistance*, thorn whip

1st level (4 slots): charm person, entangle, faery fire, thunderwave

2nd level (3 slots): barkskin*, flame sphere, hold person

3rd level (3 slots): call lightning, sleet storm, wind wall

4th level (3 slots): blight, conjure minor elementals*, grasping vine

5th level (3 slots): antilife shell, conjure elemental, mass cure wounds

6th level (1 slot): sunbeam

7th level (1 slot): reverse gravity

8th level (1 slot): earthquake

*The archmage casts resistance, barkskin and conjure minor elementals (Fire Snake 2x) spells before combat.

Quaterstaff. Melee Attack: +6 to hit, reach 5 ft., one target. Hit: 4 (1d6 + 2) piercing damage.