Archmage Battlecaster

Special Equipment. The Archmage Battlecaster wears a white robe of the archmagi (accounted for in its statistics). 

Magic Resistance. While wearing its robe of the archmagi, the Battlecaster has advantage on saving throws against spells and other magical effects.

Empowered Spell. Whenever the Battlecaster casts a spell of the evocation school by expending a spell slot, it can add its spellcasting ability modifier to the spell’s damage roll or healing roll, if any.

Potent Cantrips. The Battlecaster can add its spellcasting ability modifier to the damage it deals with any cantrip.

Spellcasting. The Battlecaster is an 18th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 21, +13 to hit with spell attacks). The Battlecaster can cast magic missile and levitate at will and has the following wizard spells prepared:

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

1st level (4 slots): detect magic, identify, shield

2nd level (3 slots): mirror image, misty step, shatter

3rd level (3 slots): counterspell, dispel magic, glyph of warding, lightning bolt

4th level (3 slots): dimension door, sickening radiance

5th level (3 slots): cone of cold, scrying, wall of force

6th level (1 slot): chain lightning, globe of invulnerability 

7th level (1 slot): prismatic spray, teleport

8th level (1 slot): illusory dragon

9th level (1 slot): foresight*

*The Battlecaster casts foresight on itself before combat.

Quarterstaff. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 4 (1d6 + 1) bludgeoning damage, or 5 (1d8+1) bludgeoning damage when used with two hands.