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 being grappled or restrained. Additionally, it ignores difficult terrain unless caused by magical effects, and cannot be knocked prone.

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 its Frightful Presence. It then uses either its Arcane Tail Machine Gun or Arcane Tail Mortar, then makes any combination of two attacks with its Arcane Claws or Arcane Guns. If neither tail weapon is available, it instead makes any combination of four attacks with those weapons.

Arcane Claw. Melee Weapon Attack: +17 to hit, reach 10 ft., one target. Hit: 20 (2d8 + 11) slashing damage plus 7 (2d6) force damage.

Arcane Gun. Ranged Weapon Attack: +12 to hit, range 120/480 ft., one target. Hit: 18 (4d6 + 4) force damage.

Arcane Tail Machine Gun (Recharge 5-6). The scorpitron sweeps a barrage in a 90-foot line that is 5 feet wide or a 30-foot cone. Each creature in the area must make a DC 21 Dexterity saving throw, taking 45 (10d8) force damage on a failed save, or half as much on a success. Creatures have advantage on the save if the scorpitron uses the cone.

Arcane Tail Mortar (Recharge 6). The scorpitron launches an energy projectile at a point it can see within 180 feet. Each creature in a 20-foot-radius area centered on that point must make a DC 21 Dexterity saving throw, taking 36 (8d8) fire damage plus 36 (8d8) force damage and falling prone on a failed save, or half as much damage and not falling prone on a 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. Each creature of the scorpitron's choice that is within 120 feet of it and aware of it must succeed on a DC 18 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the scorpitron's Frightful Presence for the next 24 hours.

Reposition Shield. The scorpitron repositions its Directional Arcane Shield.

Shield Deflection. When the scorpitron is targeted by a ranged attack or is included in the area of effect of a spell, it can reposition its Directional Arcane Shield.

The scorpitron can take 3 legendary actions, choosing from the options below. Only one option can be used at a time and only at the end of another creature's turn. The scorpitron regains spent legendary actions at the start of its turn.

Move. The scorpitron moves up to half its speed.

Reposition Shield. The scorpitron repositions its Directional Arcane Shield.

Attack (Costs 2 Actions). The scorpitron makes one Arcane Claw attack or one Arcane Gun attack.

Crushing Step (Costs 3 Actions). The scorpitron moves up to 30 feet and can move through the space occupied by Large or smaller creatures. A creature whose space the scorpitron enters must succeed on a DC 21 Dexterity saving throw or take 27 (6d8) bludgeoning damage, fall prone, and be pushed away from the scorpitron in the direction opposite its movement. On a successful save, the creature takes half as much damage, doesn't fall prone, and moves to the nearest unoccupied space without provoking opportunity attacks.