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 13). The yuan-ti can innately cast the following spells, requiring no material components:

At will: animal friendship (snakes only)

3/day: suggestion

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

Malison Type. The yuan-ti malison (type 1) has a Human body with snake head.

Multiattack. The mage makes three Arcane Burst attacks.

Arcane Burst. Melee or Ranged Spell Attack: +7 to hit, reach 5 ft. or range 120 ft., one target. Hit: 25 (4d10 + 3) force damage.

Sculpted Explosion (Recharge 4–6). The mage unleashes a magical explosion of a particular damage type: cold, fire, lightning, or thunder. The magic erupts in a 20-foot-radius sphere centered on a point within 150 feet of the evoker. Each creature in that area must make a DC 15 Dexterity saving throw. The evoker can select up to three creatures it can see in the area to ignore the explosion, as the evoker sculpts the energy around them. On a failed save, a creature takes 40 (9d8) damage of the chosen type and is knocked prone. On a successful save, a creature takes half as much damage and isn’t knocked prone.

Spellcasting. The mage is a 9th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 15, +6 to hit with spell attacks). The mage has the following wizard spells prepared:

Cantrips (at will): fire bolt, light, mage hand, prestidigitation

1st level (4 slots): detect magic, mage armor, magic missile, shield

2nd level (3 slots): misty step, suggestion

3rd level (3 slots): counterspell, fireball, fly

4th level (3 slots): greater invisibility, ice storm

5th level (1 slot): cone of cold

Displacement (Recharge 5–6). The mage projects an illusion that makes the illusionist appear to be standing in a place a few inches from its actual location, causing any creature to have disadvantage on attack rolls against the illusionist. The effect lasts for 1 minute, and it ends early if the illusionist takes damage, if it is incapacitated, or if its speed becomes 0.

Arcane Ward (Recharge 4–6). When the mage or a creature it can see within 30 feet of it takes damage, the abjurer magically creates a protective barrier around itself or the other creature. The barrier reduces the damage to the protected creature by 26 (4d10 + 4), to a minimum of 0, and then vanishes.