Multiattack. The cultist makes three attacks, using Pact Blade or Radiant Ray in any combination.
Pact Blade. Melee Attack Roll: +9, reach 5 ft. Hit: 12 (2d6 + 5) Slashing damage plus 18 (4d8) Radiant damage.
Radiant Ray. Ranged Attack Roll: +9, range 120 ft. Hit: 31 (4d12 + 5) Radiant damage.
Spellcasting. The cultist casts one of the following spells, using Charisma as the spellcasting ability (spell save DC 17):
At will: Thaumaturgy