Spellcasting. The mage is a 9th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 14, +6 to hit with spell attacks). Mary has the following Sorcerer spells prepared:

Cantrips (at will): Chill Touch, Ray of Frost, Minor Illusion, Message

1st level (4 slots): Disguise Self, Magic Missile, Shield

2nd level (3 slots): Spider Climb, Misty Step, Hold Person, Detect Thoughts, Mirror Image

3rd level (3 slots): Counterspell, Lightning Bolt, Slow, Sleet Storm

4th level (3 slots): Banishment, Polymorph, Greater Invisibility

5th level (2 slots): Cone of Cold, Telekinesis, Teleportation Circle

6th level (1 slot): Chain Lightning, Circle of Death

Immovable Mind. Mary has advantage on saving throws against being charmed or frightened

Magic Resistance. Mary Chang has advantage on saving throws against spells and other magical effects.

Huntress. Mary Chang has advantage on creatures that are half or fully submerged in water.

Genasi Legacy. Mary Chang does not need to breathe, and can cast Levitate at will.

Innate Spellcasting. Mary can cast the following spells at will, not requiring material components (Spell Save DC 18, +9 to hit with Spell attacks).

1/day each: Mind Blank, Maddening Darkness, Simulacrum, Teleport, Regenerate, Crown of Stars, Hex

Multiattack. Mary makes four attacks with her scissors.

Cursed Scissors. Melee Weapon Attack: +10 to hit, reach 5 ft. or range 20/60 ft., one target. Hit:  (2d8 + 5) piercing damage. On a critical hit, Mary can cut off an arm, leg, or any other small appendage off of a Medium or smaller creature. Immediately after attacking, Mary can teleport up to 10 feet to an unoccupied space she can see. 

Eye of Corruption (Recharge 5-6). Mary targets a creature she can see within 30 feet of her. The creature must make a DC 17 Constitution saving throw. On a failed save, it takes 5d10 necrotic damage and 5d10 poison damage. and then gains vulnerability to necrotic and poison damage for one minute. On a successful save, it takes half as much damage and does not gain the vulnerabilities.