Constructed Nightmare

 Aversion of Fire. If the construct takes fire damage, it has disadvantage on attack rolls and ability checks until the end of its next turn.

Immutable Form. The construct is immune to any spell or effect that would alter its form.

Lightning Absorption. Whenever the construct is subjected to lightning damage, it takes no damage and instead regains a number of hit points equal to the lightning damage dealt.

Magic Resistance. The construct has advantage on saving throws against spells and other magical effects.

Magic Weapons. The construct's weapon attacks are magical.

Quick Swipe. The construct can make one slam attack as a bonus action.

Spring Lock. If the construct uses it's action to wind up it's pulse strike for one round, on the next Pulse Strike attack it makes it deals an additional 18 (2d10 + 5) bludgeoning damage. If the construct choses to make a Pulse Cannon attack it loses the Spring Lock and Pulse Strikes deal normal damage.

Multiattack. The construct makes two slam attacks.

Slam. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 18 (2d10 + 5) bludgeoning damage.

Pulse Strike. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 18 (2d10 + 5) bludgeoning damage and 13 (2d8+3) thunder damage.

Pulse Cannon. (Recharge 5/6) Ranged Weapon Attack: +8 to hit, (60/120ft)., one target. Hit: 29 (4d10 + 5) thunder damage.