amethyst

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

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

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

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

Berserk. Whenever the golem starts its turn with 40 hit points or fewer, roll a d6. On a 6, the golem goes berserk. On each of its turns while berserk, the golem attacks the nearest creature it can see. If no creature is near enough to move to and attack, the golem attacks an object, with preference for an object smaller than itself. Once the golem goes berserk, it continues to do so until it is destroyed or regains all its hit points.

Multiattack. The golem makes two slam attacks.

Slam. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 19 (3d8 + 6) bludgeoning damage.

Slow (Recharge 5–6). The amethyst targets one or more creatures it can see within 10 feet of it. Each target must make a DC 17 Wisdom saving throw against this magic. On a failed save, a target can't use reactions, its speed is halved, and it can't make more than one attack on its turn. In addition, the target can take either an action or a bonus action on its turn, not both. These effects last for 1 minute. A target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

beam (Recharge 5–6). the amethyst targets any creatures it can see in a 20 foot cube. Each target must make a DC 23 dexterity saving throw against this attack. on a failed save, the targets take 3d8 damage from a purple beam and are burned for the next 3 rounds and can't be healed for the duration.