Large Construct, Chaotic Neutral

Armor Class: 16 (Natural Armor)

Hit Points: 207 (18d10+108)

Speed: 30 ft.

STR 20/+5

DEX 10/+0

CON 22/+6

INT 16/+3

WIS 14/+2

CHA 18/+4

Saving Throws: Int +7, Wis +6

Damage Resistances: Bludgeoning, Piercing, and Slashing from nonmagical attacks, Necrotic

Damage Immunities: Poison, Psychic

Condition Immunities: Exhaustion, Frightened, Paralyzed, Petrified, Poisoned

Senses: Blindsight 90 ft., Passive Perception 12

Languages: Common, Deep Speech, Sylvan, Undercommon; Understands but can’t Speak

Challenge: 12

Proficiency Bonus: +4

Drums of Fear. Nightmare Engine is a construct infused with the aberrant energies that corrupt the dreams and visions of Dreamscape. Creatures within 90 feet of the Engine hear a slow and dissonant maddening pulsation in their minds, that gives disadvantage on Concentration checks to all creatures not immune to psychic damage or the frightened condition. 

Nightmare Visions. Creatures that end their turn within 90 feet of the Engine and can see the Engine are haunted by nightmarish specters that come from their fears.
A Nightmare Vision (HP: 1; AC: 14; Blindsight, Speed: 30ft. fly; Immunity to all conditions, +4 bonus to all saving throws) can only attack the one creature they were created for (Melee spell attack +6 to hit, reach 5 ft., one target, Hit. 9 (1d10+4) psychic damage).
These Nightmare Visions play directly before their target on the initiative order, and they can only do the Attack Action and Attack of Opportunity reaction. 

Creatures immune to the frightened condition are not affected by this ability. 

• At the end of their turn, a creature can choose to close their eyes, becoming blinded until the start of their next turn, but without a Nightmare Vision appearing.
• All Nightmare Visions targeting a creature disappear if their target goes to 0 HP. 
• The nightmare visions are not affected by the negative effects of any of the Engine’s other abilities

Gears of Terror. At the start of each of its turns, the Nightmare Engine can activate one of its gears, gaining powers until the start of its next turn depending on the gear chosen. 

• Beckoning Darkness. A magical darkness envelops the area within 90 feet of the Nightmare Engine, with the area within 30 feet of the Engine being unaffected by this. Each creature that ends their turn in the magical darkness must make a DC 16 Wisdom saving throw, taking 4d6 psychic damage and becoming frightened of the Engine until the end of their next turn on a failure, or only half as much damage without being frightened on a success. 
• Restless Sleep. Each blinded creature, and each time a creature within 90 feet of the Engine becomes blinded, they must make a DC 16 Wisdom saving throw, taking 2d6 psychic damage and then going under the effects of the Sleep spell on a failure. 
• Legs of Lead. Each creature that enters the area within 90 feet of the Engine or starts its turn there must make a DC 16 Wisdom saving throw, on a failure they gain the sensation as if their legs were too heavy to walk with. They become restrained for the duration of the effect or they can take 4d6 psychic damage and only have their movement speed halved. 
• Terror Gaze. The Nightmare Engine creates a 90-foot cone coming from it and decides which way it faces. Any creature starting its turn in the area must make a DC 16 Wisdom saving throw, taking 4d6 psychic damage and becoming frightened on a failure, or only half as much damage without being frightened on a success.  

Actions.

• Cage of Unreason. Up to two creatures within 90 feet of the Nightmare Engine are immediately attacked by all of their Nightmare Visions within reach. They must also make a DC 16 Constitution saving throw, becoming stunned and taking 4d6 psychic damage at the end of each of their turns until all of their Nightmare Visions are killed or until they go to 0 HP.
  • Only two creatures can be stunned by the ability at a single time, any additional creature targeted by the ability only takes the psychic damage. 

• Piercing Horror. All creatures within 60 feet of the Nightmare Engine must make a DC 16 Wisdom saving throw, making a Nightmare Vision targeting them appear on a space within 5 feet of them and immediately making one attack against them.

Beat the Drum. The Engine stomps the ground with thundering force, amplifying the piercing sound of its drum. All creatures within 10 feet of it must make a DC 16 Dexterity Saving Throw, taking 2d10+5 Thunder damage on a failure or half as much on a success.
In addition to this, all conscious creatures within 90 feet of the Nightmare Engine must make a DC 16 Wisdom saving throw, taking 1d6 psychic damage on a failure.