Andromedon

Sensory denial. The Andromedon automatically fails (Perception) checks that rely on smell and/or hearing.

Mechanical Suit.  The Andromedon has advantage on strength checks related to breaking restraints. After the Andromedon falls bellow 40 hit points, the glass of the suit breaks and the piloting creature dies. Afterwards the suit activates "Autopilot" and fights on its own.

Autopilot. (Begins Inactive) The Andromedon cannot be healed through normal healing spells and can only use "Brutal Swing". Any creature other than a Andromedon that starts its turn or moves within 5 feet of the Andromedon must succeed on a DC 14 Dexterity saving throw or take 1d8 Acid damage. The Andromedon replaces the Psychic damage Vulnerability with Psychic damage Immunity, and gains immunity to being charmed, frightened, and unconscious. The Andromedon is no longer considered a Fiend or Demon

Brutal Swing. Melee Weapon Attack: +3 to hit, reach 5ft., one target. Hit:  34 (5d12 + 4) bludgeoning damage, and the target must succeed on a DC 20 Constitution saving throw or be stunned until the start of the Andromedon's next turn.

Hand Cannon. Ranged Weapon Attack: +7 to hit, reach 60ft., one target. Hit:  16 (3d8 + 4) piercing damage. If the target is wearing Nonmagical armor, then they must succeed on a DC 12 Dexterity or Constitution saving throw or their armor is partly destroyed and takes a permanent and cumulative −1 penalty to the AC it offers. The armor is destroyed if the penalty reduces its AC by a total of -5

Acid Cannon. (Recharge 6) Within 60ft. of the Andromedon, a glob of acid is launched that explodes within a 15 ft. radius and forcing creatures within to make a DC 15 Dexterity saving throw or take 18 (6d6) Acid damage (Half damage on success). A puddle of acid is left in a 10ft. radius for 1 minute that deals 1d8 acid damage to any creature that moves into or starts their turn within the puddle.