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 Tiny fairy creature.

Invisibility, The fiend can use its action to turn invisible, attacking a creature or casting a spell will cause the invisibility to break.

Multi-attack, The fiend can make 2 claw attacks as an action

Claw (Fiend Form Only). Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 10 (2d6 + 3) slashing damage.

Command (at will), cast the spell command, target must make a DC 15 wisdom save.

Suggestion (at will), cast the spell suggestion, target must make a DC 15 wisdom save.

Hold person (3/day), cast the spell hold person, target must make a DC 15 wisdom save.

Dimension door (3/day), cast the spell dimension door

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 Bite. The fiend bites a creature charmed by it or a willing creature. The target must make a DC 15 Constitution saving throw against this magic, taking 21 (3d10 + 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.

Legendary Resistance (1/Day). If the fiend fails a saving throw, it can choose to succeed instead.