Archmage

Medium humanoid (any race), any alignment

Armor Class 12 (15 with mage armor)
Hit Points 99 (18d8 + 18)
Speed 30 ft.

Saving Throws Int +9, Wis +6
Skills Arcana +13, History +13
Damage Resistance damage from spells; nonmagical bludgeoning, piercing, and slashing (from stoneskin)
Senses passive Perception 12
Languages any six languages
Challenge 12 (8,400 XP)

Magic Resistance. The archmage has advantage on saving throws against spells and other magical effects.
Spellcasting. The archmage is an 18th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 17, +9 to hit with spell attacks). The archmage can cast disguise self and invisibility 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, mage armor, magic missile
2nd level (3 slots): detect thoughts, mirror image, misty step
3rd level (3 slots): counterspell, fly, lightning bolt
4th level (3 slots): banishment, fire shield, stoneskin
5th level (3 slots): cone of cold, scrying, wall of force
6th level (1 slot): globe of invulnerability
7th level (1 slot): teleport
8th level (1 slot): mind blank
9th level (1 slot): time stop
The archmage casts mind blank, stoneskin and magic armor* spells on itself before combat.

Actions

Dagger. Melee or _Ranged Weapon Attack:__ +6 to hit, reach 5 ft. or range 20/60 ft., one target. _Hit: 4 (1d4 + 2) piercing damage.

Description

Archmages are powerful (and usually quite old) spellcasters dedicated to the study of the arcane arts. Benevolent ones counsel kings and queens, while evil ones rule as tyrants and pursue lichdom. Those who are neither good nor evil sequester themselves in remote towers to practice their magic without interruption. An archmage typically has one or more apprentice mages, and an archmage's abode has numerous magical wards and guardians to discourage interlopers.