Special Equipment. The Stranger wears an invisible ring of mind shielding that thwarts magical attempts to read their thoughts. The Stranger also wears dimensional shackles but is eager to be rid of them. One touch from Omid's mace-key causes the shackles to fall off, freeing the Stranger.
Magic Resistance. The Stranger has advantage on saving throws against spells and other magical effects.
Spellcasting. The Stranger 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 Stranger casts these spells on itself before combat.
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.