Cultist, 2nd-level Warlock

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

Pact Magic. The cultist is a 1st level warlock and gets the following spells (spell save DC 12, +4 to hit with spell attacks) as a result:

Cantrips (at Will): Eldritch Blast, Minor Illusion, spare the dying

1st Level (2 Slots): Charm Person, Hex, Expeditious Retreat

Among the Dead

The Cultist has advantage on saving throws against any disease. Additionally, undead have difficulty harming it. If an undead targets it directly with an attack or a harmful spell, that creature must make a Wisdom saving throw against the spell save DC. On a failed save, the creature must choose a new target or forfeit targeting someone instead, potentially wasting the attack or spell. On a successful save, the creature is immune to this effect for 24 hours. An undead is also immune to this effect for 24 hours if the cultist targets it with an attack or a harmful spell.

Eldritch Invocations

In their study of occult lore, the cultist has unearthed eldritch invocations, fragments of forbidden knowledge that imbue it with an abiding magical ability.

Agonizing Blast.When casting eldritch blast, add the Charisma modifier to the damage it deals on a hit.

Mask of Many Faces. Can now cast disguise self at will, without expending a spell slot.

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