Small Construct/Aberration, Chaotic Evil

Armor Class: 16 (Natural Armor)

Hit Points: 123 (19d6+57)

Speed: 20 ft.

STR 14/+2

DEX 17/+3

CON 16/+3

INT 8/-1

WIS 14/+2

CHA 13/+1

Skills: Performance +4
Saving Throws: Con +6, Wis +5

Damage Resistances: Poison, Thunder

Condition Immunities: Prone

Senses: Blindsight 60 ft., Passive Perception 12

Languages: Common

Challenge: 6

Proficiency Bonus: +3

Flesh and Clockwork. This creature is an ungodly combination of organic and mechanical parts that feeds on other creatures to try to assemble a real and beautiful body for itself. It is considered both Construct and Aberration, and is affected by effects that work on either. 

Compressed Body. Most of this creature’s fleshy and grotesque body is usually hidden inside of a beautiful tiny music box. The music box is also one of its parts, and is indistinguishable from a normal music box, both in appearance and function, while the creature is motionless and hidden inside. While it is in its tiny music box form, this creature can use all of its abilities, but it has no movement speed and attacks against it have advantage.
It can change into and from this form using a bonus action. 

Jingles and Bells. At the start of each of its turns, if it is not restrained or incapacitated, the Merry Music Box can decide to start turning its crank and a winter christmas song begins playing. It can choose one of several types of tunes, and all creatures that are not deafened by magical means within 30 feet of it are affected by its effects.

• Lullaby. If a creature ends their turn in the area, they must make a DC 15 Wisdom saving throw, going under the effects of the Sleep spell on a failure for 1 hour, or until woken up.
• Jingle. If a creature enters the area for the first time or starts their turn there, they must make a DC 15 Wisdom saving throw. On a failure, they are forced to dance and skip to the lighthearted tune of the melody, losing half of their movement speed until the end of their next turn. 
• Last Wham! All creatures in the area begin to feel a gripping feeling around their heart. Each time they attack or cast a spell or do some other strenuous activity in the area, they take 1d6 necrotic damage.  

Actions. 

• Audio Feedback. Merry Music Box starts turning its crank rapidly, and an ear shattering and distorted mechanical sound is emitted. Each creature in a 30-foot cone must make a DC 15 Constitution saving throw. A creature takes 3d6 thunder damage on a failure, or half as much on a success. A creature can decide to take double the amount of damage from this ability, but they become deafened until the end of the box’s turn. 
• Gathering of Kin. Melee Weapon Attack: +6 to hit, reach 10 ft., one target. Hit: 12(2d8+3) slashing damage plus extra 7 (2d6) necrotic damage. Merry Music Box gains Temporary Hit Points equal to the damage dealt if the target is a living creature.
  Merry Music Box starts carving a creature’s flesh and adding it to its own with its elongated arms; it prefers to use this feature against unconscious creatures. 
• Bridge and Chorus. Merry Music Box starts turning the crank more slowly and somberly, only to crescendo into a bombastic finale. Merry Music Box will deal double the amount of damage with all of its abilities and features during its next turn, and their DC will be increased by 3.