Telepathic Bond. The fiend ignores the range restriction on its telepathy when communicating with a creature it has charmed. The two don't even need to be on the same plane of existence.

Shapechanger. The fiend can use its action to polymorph into a Small or Medium humanoid, or back into its true form. Without wings, the fiend loses its flying speed. Other than its size and speed, its statistics are the same in each form. Any equipment it is wearing or carrying isn't transformed. It reverts to its true form if it dies.

Companion's Calling. Twice per day, another member of the Wicked Hand can summon the Ace of Hearts to their location, and she can then teleport herself and that member back to her original location, or, once per day, she can teleport herself and one willing creature to any location she has been to on the Plane they are currently on.

Diabolical Sorcerer. The Ace of Hearts is considered a 5th Level Sorcerer, and all of her fire-based spells use Hellfire, which ignores fire resistance and treats fire immunity as resistance.

6 Sorcery Points - Careful Spell, Empowered Spell
5 Cantrips - Chill Touch, Fire Bolt, Frostbite, Infestation, Message
6 Spells (Slots 4/3/2):
Level 1 - Burning Hands, Chaos Bolt, Ray of Sickness
Level 2 - Aganazzar's Scorcher, Enlarge/Reduce
Level 3 - Fireball

Claw (Fiend Form Only). Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 6 (1d6 + 3) slashing damage.

Flame Tongue Shortsword. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 9 (1d6 + 5) piercing damage. As a bonus action, a command word can be spoken to cause flames to erupt from the blade. These flames shed bright light in a 40-foot radius and dim light for an additional 40 feet. While the sword is ablaze, it deals an extra 2d6 fire damage to any target it hits. The flames last until you use a bonus action to speak the command word again or until you drop or sheathe the sword.

Charm. One humanoid the fiend can see within 30 feet of it must succeed on a DC 15 Wisdom saving throw or be magically charmed for 1 day. The charmed target obeys the fiend's verbal or telepathic commands. If the target suffers any harm or receives a suicidal command, it can repeat the saving throw, ending the effect on a success. If the target successfully saves against the effect, or if the effect on it ends, the target is immune to this fiend's Charm for the next 24 hours.

The fiend can have only one target charmed at a time. If it charms another, the effect on the previous target ends.

Draining Kiss. The fiend kisses a creature charmed by it or a willing creature. The target must make a DC 15 Constitution saving throw against this magic, taking 32 (5d10 + 5) psychic damage on a failed save, or half as much damage on a successful one. The target's hit point maximum is reduced by an amount equal to the damage taken. This reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hit point maximum to 0.

Etherealness. The fiend magically enters the Ethereal Plane from the Material Plane, or vice versa.

Infernal Heartbreaker. Wand/Revolver: +5 to hit, range 120 ft., one target. Hit: 14 (4d6) Fire damage. DC 12 Constitution saving throw or target is Stunned for one round. 6 uses per day.

Hellish Rebuke. You point your finger, and the creature that damaged you is momentarily surrounded by hellish flames. The creature must make a Dexterity saving throw. It takes 2d10 fire damage on a failed save, or half as much damage on a successful one. This fire ignores fire resistance, and treats fire immunity as resistance.

At Higher Levels. When you cast this spell using a spell slot of 2nd level or higher, the damage increases by 1d10 for each slot level above 1st.