Multiattack. The cultist makes three Pact Axe attacks.
Pact Axe. Melee Attack Roll: +7, reach 5 ft. Hit: 10 (1d12 + 4) Slashing damage plus 13 (3d8) Fire damage.
Spellcasting. The cultist casts one of the following spells, using Wisdom as the spellcasting ability (spell save DC 15, +7 to hit with spell attacks):
At will: Scorching Ray (level 5 version), ThaumaturgyHellish Rebuke. The cultist casts Hellish Rebuke in response to that spell's trigger, using the same spellcasting ability as Spellcasting.