Arcana Golem

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.

The golem's creator, if within 60 feet of the berserk golem, can try to calm it by speaking firmly and persuasively. The golem must be able to hear its creator, who must take an action to make a DC 15 Charisma (Persuasion) check. If the check succeeds, the golem ceases being berserk. If it takes damage while still at 40 hit points or fewer, the golem might go berserk again.

Aversion of Force. If the arcana golem takes force damage, it has disadvantage on attack rolls and ability checks until the end of its next turn.

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

Lightning Absorption. Whenever the arcana golem 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 arcana golem has advantage on saving throws against spells and other magical effects.

Magic Weapons. The arcana golem's weapon attacks are magical.

Magic Dependence.  If Dispel Magic is cast on the arcana golem it must succeed on a DC 10 Constitution saving throw or be destroyed. 

Spellcasting. The arcana golem is a 5th level spellcaster. It's spellcasting ability is Intelligence (Spell Save DC: 15, Spell Attack Modifier: +3). It has the following wizard spells prepared:                                                                                                                                                  Cantrips (At Will): Dancing Lights, Prestidigitation, Thunderclap, Toll the Dead                                                                1st Level (4 slots): Catapult, Chromatic Orb, Detect Magic, Earth Tremor                                                                                     2nd Level (3 slots): Flaming Sphere, Shatter                                       3rd Level (2 slots): Animate Dead

Multiattack. The golem makes two slam attacks.

Slam. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 13 (2d8 + 4) bludgeoning damage.