Dark Devotion. The cultist has advantage on saving throws against being charmed or frightened.

Aberrant mutation: the aberrant cultist has developed  a mutation from spending so much time in the presence of aberration  roll a d6 and look at the table below

1-2 chitinous armor:the cultist has developed strange natural armor add +2 to ac

3-4 tumorous arm: one of the cultists arms has been terribly mutated adding a club attack that does 1d8+3 damage with a +4 to hit 

5-6 second head: the cultist has a hideous second head that whispers far Realm secrets to anyone within 20 ft. anyone that enters within 20 ft of the cultist that is not a fellow cultist must make a DC 13 wisdom saving throw or take 2d6 psychic damage. 

Scimitar. Melee Weapon Attack: +3 to hit, reach 5 ft., one creature. Hit: 4 (1d6 + 1) slashing damage.