Actions

Multi-Attack. The Possessed Daemon Engine makes two melee weapon attacks per turn.
Crush. Melee Weapon Attack, one target, 5ft range, +13 to hit. Hit: 3d8 +8 Bludgeoning Damage and the creature becomes Grappled and restrained, (Break DC 23). While a creature is Grappled by the Possessed Daemon Engine, its can only make melee attacks against the grappled creature and makes Crush attacks at advantage.
Sweep. Melee Weapon Attack, up to three targets, 5ft range, +13 to hit. Hit: 2d8+8 Bludgeoning damage.
Momentous Charge (1 Charge) [recharge 5-6]. The Possessed Daemon Engine moves a minimum of 15ft in a straight line towards a target before slamming into the victim, Imposing a DC16 Dexterity Save. Creatures that are Large or smaller make this save at Disadvantage, taking 10d6+8 on a failed save

Reactions

Rapid Discharge (1 Charge). As a reaction to an incoming attack, the Possessed Daemon Engine Sends a powerful bolt of lightning at either an incoming projectile, attempting to disrupt its trajectory or a Melee attacker.
Ranged Attack - The Possessed Daemon Engine Gains an additional 5 AC against the attack and critical damage becomes regular damage instead.
Melee Attack - Blasting the attacker with a bolt of lightning, it imposes a DC16 Dexterity Saving Throw against the attack dealing 3d8 Lightning damage on a fail and half that on a success.

Legendary Actions

The Possessed Daemon Engine has 3 Legendary actions that it can spend at the end of any other creature's turns.   Tase (1 action, 1 Charge). Ejecting a blast of electrical power towards a single target, the Possessed Daemon Engine attempts to shock a creature into a prone state, imposing a DC16 Constitution Saving Throw. Creatures that fail this save are knocked prone and take 2d12 Lightning damage, creatures that pass this save take half of this damage and are not knocked prone.   Overcharge (2 Actions, 2 Charges). Destroying its own circuitry and motors in the process, the Possessed Daemon Engine makes a burst of movement. Taking 4d6 Fire damage, it may immediately move up to 30ft and make a single melee attack against one creature.

Lair Actions

Within its Lair, a Possessed Daemon Engine has a rotation of abilities that it cycles through at an initiative of 20.

1. Summon Lesser Daemon Engines. Summoning 3d6 +6 Lesser Daemon Engines to the battle, dropping from the ceiling, they appear on, or within 5ft of the Possessed Daemon Engine.
2. Interference Order. Giving a direct order to the Lesser Daemon Engines, it commands them to use their bodies to protect their slave-driver. all attacks made against the Possessed Daemon Engine this round are made at Disadvantage, ignoring all other modifiers.
   Attacks that miss instead deal normal weapon damage to the Lesser Daemon Engines protecting it as if the weapon had the Cleaving property.
3. Repair Order. Issuing a repair order, the drones immediately respond, restoring an amount of hit points to the Possessed Daemon Engine equal to 1d4 for each Lesser Daemon Engine alive.
4. Salvage Order. Their task over, the Lesser Daemon Engines begin to dismantle themselves, transferring their leftover dregs of energy to the Possessed Daemon Engine. The Possessed Daemon Engine gains 1 Charge for every 2 Lesser Daemon Engines commanded to Salvage.

The dockyards that these goliaths traverse are filled with scrap yet to be cleared, cargo to load and backup fuel cells. Where the smell of grease and oil meets sulfur and vinegar, the Lesser Daemon Engines now work alongside their once docile master to enact its revenge.   A Possessed Daemon Engine within its Lair is a CR16 Encounter.