Aurinoir Destroyer

Legendary Resistance (3/day). When the Aurinoir Destroyer fails a saving throw, it can choose to succeed instead.

Magic Resistance. The Aurinoir Destroyer has advantage on saving throws against spells and magical effects. 

Immutable Form. The Aurinoir Destroyer is immune to all spells and magical effects that attempt to alter it's form.

Attuned Proto-Soul. Through its proto-soul, the Aurinoir Destroyer can be semi-attuned to up to five magical items. While connected in this way, the Destroyer knows the precise location on the item and prevents creatures from attuning to it, though the Destroyer gains no attunement benefit from the items.

Magic Weapons. The Destroyer's weapon attacks are considered magical.

Multiattack. The Aurinoir Destroyer makes three attacks with its Hook Blade. It can forgo one of these attacks to make a Harpoon attack instead, or use its Electroshock action.

Hook Blade. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 18 (3d6 + 7) [slashing] damage, and the target is grappled (escape DC19). The Destroyer can have a maximum of two creatures grappled in this way. 

Harpoon. Ranged Weapon Attack: +14 to hit, range 120 ft., one target. Hit: 21 (3d8 + 7) [piercing] damage, and the creature is harpooned. Only one creature can be harpooned at a time, while harpooned the creature's movement speed is 0. A creature can use it's action to remove the harpoon, taking 14 (3d8) piercing damage in the process. While a creature is harpooned, the Destroyer can use this attack again to partially recall the harpoon. A harpooned creature must succeed a DC21 Strength saving throw or be pulled 60ft towards the Destroyer. If a creature breaks free of the harpoon, it is recoiled back rapidly. Ready to be launched again.

While the Harpoon is deployed, the steel cable can be attacked and cut, preventing the Destroyer from using this action again. It has an AC of 18 and 40HP.

Electroshock. The Aurinoir Destroyer targets a creature harpooned by it, sending a current of overwhelming electricity through the harpoon's steel cable. The harpooned creature takes 45 (10d8) lightning damage and must succeed a DC20 Constitution saving throw or be stunned until the end of their next turn.

Opportunity Attack. The Destroyer takes an opportunity attack using one of it's attack actions.

Onslaught (Costs 1 Actions). The Aurinoir Destroyer makes a Hook Blade or Harpoon attack.

Blast Thrusters (3/Day). The Aurinoir Destroyer jumps up to 50ft away in a blast of alchemical thruster fire. Creatures within 5ft of it when it begins this action must make a DC17 Dexterity saving throw, taking 14 (4d6) fire damage on a failed save, or half as much on a successful one. Creatures in it's landing area must make a DC17 Dexterity saving throw or take 35 (10d6) bludgeoning damage and be knocked prone. 

Creatures that are knocked prone are restrained (escape DC19) until the Destroyer moves away, cannot be targeted by the Destroyer's attacks, and take 14 (4d6) bludgeoning damage at the start of each of the Destroyer's turns.