Billy

Incorporeal Movement. Billy can move through other creatures and objects as if they were difficult terrain. He takes 5 (1d10) force damage if he ends his turn inside an object.

Devil’s Sight. Billy can see normally in darkness, both magical and nonmagical, to a distance of 120 ft.

Grasp of Hadar. Once on each of his turns when Billy hits a creature with his eldritch blast, he can move that creature in a straight line 10 feet closer to him.

Scream of Rest. 1d6
If Billy or any friendly creatures who can hear his death metal performance regain hit points at the end of the short rest by spending one or more Hit Dice, each of those creatures regains an extra 1d6 hit points.

Spellcasting. Billy is a 7th-level spellcaster. His spellcasting ability is Charisma (spell save DC 15, +7 to hit with spell attacks). Billy has the following warlock and bard spells prepared:

Cantrips (at will): Eldritch blast; Chill touch; Prestidigitation; True Strike; Vicious mockery

1st level spells (4 spell slots + 2 pact magic): Bane; Dissonant whispers; Healing word; Hex; Inflict wounds; Tasha's hideous laughter

2nd level spells (3 spell slots): Hold person; Misty step;  Shatter

3rd level spells (2 spell slots): Bestow curse; Fear

Withering Touch. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 17 (4d6 + 3) necrotic damage.

Etherealness. Billy enters the Ethereal Plane from the Material Plane, or vice versa. He is visible on the Material Plane while it is in the Border Ethereal, and vice versa, yet he can't affect or be affected by anything on the other plane.

Bardic Inspiration. 1d8
A creature within 60 ft. that can hear Billy gains an inspiration die (1d8). For 10 minutes, the creature can add it to one ability check, attack roll, or saving throw. This can be added after seeing the roll, but before knowing the outcome. (4/Short Rest)

Ethereal Embrace. up to 3d6
Billy has a 3d6 damage pool that resets when he finishs a long rest. Whenever he deals damage to a creature, as a bonus action, he may choose to deal an additional amount of d6 necrotic damage to one creature he can see within 60 ft. (3/Long Rest). A successful Wisdom saving throw (Spell DC 15) halves this damage.