Spellcasting. The Knight is a 19th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 15, +7 to hit with spell attacks). The knight has the following wizard spells prepared:
Cantrips (at will): fire bolt, light, mage hand, shocking grasp 
1st level (4 slots): detect magic, mage armor, magic missile, shield 
2nd level (3 slots): misty step, suggestion 
3rd level (3 slots): counterspell, fireball, fly 
4th level (1 slots): greater invisibility, ice storm

Second Wind (Recharges after a Short or Long Rest). As a bonus action, the Knight can regain 20 hit points.

Multiattack. The knight makes three melee attacks. 
Greatsword. Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 12 (2d6 + 5) slashing damage. 
Heavy Crossbow. Ranged Weapon Attack: +4 to hit, range 100/400 ft., one target. Hit: 5 (1d10) piercing damage.