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

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

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

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

Multiattack. The guardian makes two Fist Slams -OR- one Sword Arm Sweep, -OR- one Elemental Blast attack.

Fist Slam. Melee Weapon Attack: +14 to hit, reach 5 ft., one target. Hit: 18 (2d8 + 8) points of bludgeoning damage.

Sword Arm Sweep. Melee Weapon Attack: +14 to hit, reach 10 ft., up to two targets within range. Hit: 25 (3d10 + 8) points of slashing damage. On a hit they must make a DC 20 STR Save or be pushed at a 90 degree angle 20 feet from where they are in relation to the guardian and then must make a DC 18 DEX save or fall prone. If they hit a wall or solid object during that 20 feet of movement they then take an additional 7 (2d6) points of bludgeoning damage and do not make the DEX Saving throw and are not knocked prone.

Elemental Blast. (Recharge on a 5-6) The golem creates a blast of energy of either Lightning, Acid, Cold, or Fire (Choice 1) between 10 and 60 feet of itself within a 5 ft cube in 2 locations. (Each cube must be at least 15 feet apart but no further than 40 feet from the other) . Each creature in the space and within 5 ft of that cube area must make a DC 18 DEX saving throw, taking 20 (3d8 + 7) points of the elemental type damage on a failed save, or half as much damage on a successful one.

If making an opportunity Attack it does so with it's Fist Slam attack

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

Movement. Can use 1 Legendary Action to move up to its full movement speed.

Armor Empowerment: Can use 2 Legendary actions to increase it's AC by 3 until the end of it's next turn.

Arm Sweep: Can use 3 Legendary Actions to make a Sword Arm Sweep attack.