Multiattack. The knight makes two attacks, using Greatsword or Heavy Crossbow in any combination.
Greatsword. Melee Attack Roll: +5, reach 5 ft. Hit: 10 (2d6+ 3) Slashing damage plus 4 (1d8) Radiant damage.
Heavy Crossbow. Ranged Attack Roll: +2, range 100/400 ft. Hit: 11 (2d10) Piercing damage plus 4 (1d8) Radiant damage.
Parry. Trigger: The knight is hit by a melee attack roll while holding a weapon. Response: The knight adds 2 to its AC against that attack, possibly causing it to miss.