Boiler Man

Unending Clock: Boiler Men have inherent immunities due to their Clockwork bodies.

Immune to Stun, Blind, Petrify, Fear, Poison, Diseases, Deafen, and Exhaustion.

Towering Form: Boiler men count as two sizes larger when engaging in combat.

Coup De Grace:  As an action you may use a melee or ranged weapon to deliver a coup de grace to an incapacitated or grappled creature within 5 feet of you. Your coup de grace is a special attack that automatically hits and scores a critical hit, and may also kill the target outright. (this attack counts as an automatic critical hit, however, upon successful Coup De Grace, its movement speed is reduced to 0 for the next two turns.)

Concussive Blows:  Whenever a Boiler Man delivers an unarmed attack against an enemy in heavy armor, add a +10 to it's attack roll.

Heavy Handed:  Whenever a Boiler Man delivers an unarmed attack against an enemy, they must roll above a 10 CON saving throw or become Grappled. 

Heart of Coal: Being grappled by a Boiler Man deals 3 fire damage for every turn an enemy remains grappled.

Unarmed Attack. Iron Fists d20 + 10  to hit, reaches up to 10 ft. and up to two targets may be attacked with the same action. Hit: 2d20 + STR modifier of Bludgeoning damage. 

Ranged Attack #1. Gauss Rifle: 1d20+10 to hit, with a range of 125 ft. and launching at a single target. Hit:  8d8 + 10) of piercing damage plus an extra 20 electrical damage.

Ranged Attack #2. Steam breath: Targets must make a 19 CON saving throw or take 10d10 of fire damage.

Integrated Weapon Attack: Wrist Blade: d20 + 20 to hit, reaches 5 ft. Can only target one opponent (Multi-Attack: Can be used to attack the same target on a successful Critical strike) Hit: 6d10 per hit of Slashing damage + 15 points of electrical damage.

Vent Coolant: When attacked from behind, the Boiler Man can release a 30ft. sphere of cold centered on its own body. Targets inside this sphere must make a DEX saving throw of 20 - their CON save modifier or become knocked prone and become slowed.

Vent Steam: When attacked from the front, the Boiler Man can release a 20ft. cone of heat from it's chest, enemies within this cone must make a CON saving throw of 18 or take 6d8 of fire damage, and become blinded until the end of their next turn.

Once per turn, and once after an attack on itself. Boiler Man can use a reactionary attack.

Burning Oil (Costs 1 Action). Six times per day, A Boiler Man can exude a caustic gas from its pipes, which cover 350ft moving around corners, and causing living enemies vision to lower to 5ft. (those with Blindsight or are Constructs themselves are unaffected) Enemies within this field are considered nearly blind, gain disadvantage on attacks, and take 2 points of fire damage with each turn they are inside this fog. 

Discharge (Costs 1 Action) Once per turn, at the end of it's turn, the Boiler man can launch a volley of scalding oil at an opponent within 20 feet, target must make a DEX saving throw of 15 or take 40 points of fire damage and become lose access to magic items.

Unbreakable Mechanism (Costs 1 Actions) Once per turn, and at the end of an attack the Boiler Man can use it's legendary action to automatically repair 2d20+CON of any damage except core damage.