Scorpitron

Construct Nature. The scorpitron doesn't require air, food, drink, or sleep.

Eight-Legged Siege Engine. The scorpitron has Advantage on saving throws against the Grappled and Restrained conditions. Additionally, it ignores difficult terrain unless caused by magical effects.

Legendary Resistance (3/Day). If the scorpitron fails a saving throw, it can choose to succeed instead.

Arcane Plating and Armament. The scorpitron has Advantage on saving throws against spells and other magical effects, and Resistance to damage from spells (Lightning damage from spells is taken normally, without either Resistance or Vulnerability). Whenever the scorpitron takes Force damage, half that damage (before Resistance) is reflected to one hostile creature of the scorpitron's choice within 60 feet. The scorpitron's Arcane Claws and Arcane Guns are +2 magical weapons.

Directional Arcane Shield. The scorpitron projects a 25-foot-wide, 25-foot-tall magical barrier that appears as a translucent light-blue surface. The barrier originates from the edge of the scorpitron's space, moves with it, and can face any direction, remaining fixed even if the scorpitron turns. The scorpitron can activate or deactivate the barrier as a Bonus Action and, while active, can change its direction with a Bonus Action, Legendary Action, or the appropriate Reaction. Projectiles (even magical ones), ranged spell attacks, and areas of effect of spells cannot pass directly through the barrier. If such an effect hits the barrier it deals no damage to the scorpitron, but if the barrier is reduced to 0 hit points, any remaining damage is dealt to the scorpitron. The barrier has 450 hit points, regains 30 hit points at the start of the scorpitron's turn, and is vulnerable to Force damage. The barrier does not block movement through it or melee attacks.

Multiattack. The scorpitron uses Frightful Presence. It then uses either Arcane Tail Machine Gun or Arcane Tail Mortar, then makes two attacks, using Arcane Claw or Arcane Gun in any combination. If neither tail weapon is available, it makes four attacks, using Arcane Claw or Arcane Gun in any combination

Arcane Claw. Melee Attack Roll: +17, reach 10 ft. Hit: 20 (2d8 + 11) Slashing damage plus 7 (2d6) Force damage.

Arcane Gun. Ranged Attack Roll: +12, range 120/480 ft. Hit: 18 (4d6 + 4) Force damage.

Arcane Tail Machine Gun (Recharge 5-6). Dexterity Saving Throw: DC 21, each creature in a 90-foot long and 5-foot wide line or a 30-foot cone. If the cone is used, creatures have advantage on the Saving Throw. Failure: 45 (10d8) Force damage. Success: Half damage.

Arcane Tail Mortar (Recharge 6). The scorpitron launches an energy projectile to a point it can see within 180 feet of itself. Dexterity Saving Throw: DC 21, each creature 20-foot-radius Sphere centered on that point. Failure:  36 (8d8) Fire damage plus 36 (8d8) Force damage, and the creature has the Prone condition. Success: Half damage only. Failure or Success: The area ignites until the start of the scorpitron's next turn, a creature that enters the area or starts its turn in it takes 7 (2d6) Fire damage.

Frightful Presence (1/Day). The scorpitron casts Fear, requiring no Verbal, Somatic, or Material components and using Strength as the spellcasting ability (Spell save DC 17).

Reposition Shield. The scorpitron repositions its Directional Arcane Shield.

Shield Deflection. Trigger: The scorpitron is targeted by a ranged attack or is included in the area of effect of a spell. Response - The scorpitron repositions its Directional Arcane Shield.

Legendary Action Uses: 3. Immediately after another creature's turn, the scorpitron can expend a use to take one of the following actions. The scorpitron regains all expended uses at the start of each of its turns.

Crushing Step. The scorpitron moves up to half its speed and can move through the space occupied by Large or smaller creatures. Dexterity Saving Throw: DC 21, all creatures whose space the scorpitron enters. Failure: 18 (4d8) Bludgeoning damage, and the creature has the Prone condition and is pushed away from the scorpitron in the direction opposite its movement. Success: Half damage only, and the creature moves to the nearest unoccupied space without provoking Opportunity Attacks. Failure or Success: The scorpitron can't take this action again until the start of its next turn.

Pounce. The scorpitron moves up to half its speed, and it makes one Arcane Claw attack or one Arcane Gun attack. The scorpitron can't take this action again until the start of its next turn.

Reposition Shield. The scorpitron repositions its Directional Arcane Shield.