Captain Bloodhelm

 Ghostly Duelist: Captain Bloodhelm deals an extra damage dice when using a finesse weapon.

Ethereal Sight. The ghost can see 60 feet into the Ethereal Plane when it is on the Material Plane, and vice versa.

Magic Resistance. Bloodhelm has advantage on saving throws against spells and other magical effects.

Incorporeal Movement: The ghost can move through other creatures and objects as if they were Difficult Terrain. It takes 5 (1d10) force damage if it ends its turn inside an object.

Legendary Resistance (3/Day). If the dragon fails a saving throw, it can choose to succeed instead.

Spellcasting: Captain Bloodhelmis a 17th-level Spellcaster. Its Spellcasting Ability is Charisma (spell save DC 22, +15 to hit with spell attacks). Captain Blooodhelm has the following Warlock spells Spells prepared: 

Cantrips (at will): toll the dead, eldritch blast, mage hand, minor illusion 
1st-5th level (4 5th-level slots): Dimension Door, Blight, tounges, summon undead, fear, fly, misty step, invisibility, hold person, darkness, distort value, armor of Agathy.

Mystic Arcanum (1/day): Circle of death, Firger of death, Maddning darkness, True polymorph. 

Cutlass. Melee attack +12 to hit, 5ft., one target 10 (2d6+6) piercing damage and 18 (4d6) necrotic damage.

Blunderbuss. Ranged attack +12 to hit., one target 16 (1d10+6) piercing damage and 18 (4d6) necrotic damage.

Eldritch Blast. Spell attack +15 to hit, 300ft range., four blasts., hit: 11 (1d10+6) force damage, and the target is thrown 10ft away. 

Horrifying Visage: Each non-undead creature within 60 ft. of the ghost that can see it must succeed on a DC 19 Wisdom saving throw or be Frightened for 1 minute. If the save fails by 5 or more, the target also ages 1d4 x 10 years. A Frightened target can repeat the saving throw at the end of each of its turns, Ending the Frightened condition on itself on a success. If a target's saving throw is successful or the effect ends for it, the target is immune to this ghost's Horrifying Visage for the next 24 hours. The aging effect can be reversed with a Greater Restoration spell, but only within 24 hours of it occurring.

Possession (Recharge 6): One Humanoid that the ghost can see within 5 ft. of it must succeed on a DC 22 Charisma saving throw or be possessed by the ghost; the ghost then disappears, and the target is incapacitated and loses control of its body. The ghost now controls the body but doesn't deprive the target of awareness. The ghost can't be targeted by any attack, spell, or another effect, except ones that turn undead, and it retains its alignment, Intelligence, Wisdom, Charisma, and immunity to being Charmed and Frightened. It otherwise uses the possessed target's statistics but doesn't gain access to the target's knowledge, Class Features, or Proficiencies.
The possession lasts until the body drops to 0 Hit Points, the ghost ends it as a Bonus Action, or the ghost is turned or forced out by an Effect like the Dispel Evil and Good spell. When the possession ends, the ghost reappears in an unoccupied space within 5 ft. of the body. The target is immune to this ghost's Possession for 24 hours after succeeding on the saving throw or after the possession ends.

Parry: Captain Bloodhelm can add +5 to his AC against one melee attack.

Bloodhelm can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. Bloodhelm regains spent legendary actions at the start of their turn.

Attack. Captain Bloodhelm makes an attack.

Reload. Captain Bloodhelm reloads his pistol.

Move. Captain Bloodhelm moves his speed.

Ghost of the Slain. Captain Bloodhelm summons 1d6+2 shadows.