Arcane Form. Creatures within 10 feet of Xillo have disadvantage on saving throws against his spells.

Magic Resistance. Xillo has advantage on saving throws against spells

Spellcasting. The mage is a 9th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 16, +8 to hit with spell attacks). The mage has the following wizard spells prepared:

Cantrips (at will): Firebolt, Arcane Shard, Sensify, Shadow Thrust, Mind Sliver, Frostbite

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

2nd level (3 slots): Sinkhole, Snowball Swarm

3rd level (3 slots): Slow, Counterspell

4th level (3 slots): Blight, Dimension Door

Arcane Shard. Ranged Spell Attack: +8 to hit, range 60 ft., one target. Hit: 6 (2d6) slashing damage.

Firebolt. Ranged Spell Attack: +8 to hit, range 120 ft., one target. Hit: 10 (2d10) fire damage.

Sensify. Single Target Charisma Saving Throw, DC 16. On a fail a target takes 2d6 psychic damage. Additionally the target has disadvantage on the next saving throw against blindness or deafness, or vulnerability to thunder damage (whichever comes first).

Shadow Thrust. Single Target Strength Saving Throw, DC 16. On a fail a target takes 2d6 psychic damage. If the target is blinded or in darkness they instead take 2d10 psychic damage.

Mind Sliver. Single Target Intelligence Saving Throw, DC 16. On a fail a target takes 2d6 psychic damage. Additionally the target subtracts 1d4 from the next saving throw they make.

Frostbite. Single Target Constitution Saving Throw, DC 16. On a fail a target takes 2d6 cold damage. Additionally the target has disadvantage on the next attack roll that they make.

Quicken Spell (Recharge 5-6). Xillo casts a leveled spell as a bonus action.

Xillo can take two legendary actions from the following list. He regains all spend uses at the end of his turn. 

Cast a Cantrip. Xillo casts one of his cantrips
Seal. Xillo traps a creature in a barrier of abjuration magic. The next time that creature attempts to move it must make a strength saving throw against Xillos spell save DC. On a failure the creature cannot take a move action or the dash action on this durn.