Arcane Golem

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 spells and other magical effects.

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

Multiattack. The golem makes two claw attacks.

Claw. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 13 (2d6 + 5) slashing damage.

Arcane Blast . The golem targets one creature it can see within 60' with a ray of magical energy rolled randomly on the table below;
1-Fire Ray- A blast of super-heated fire blasts outward from its hand doing 4d6 fire damage and igniting flammable material. DC 14 Dex save for half. Target must spend 1 turn to put out fire
2-Ice Ray- A Ray of pure cold blasts outward from its hand doing 3d8 cold damage DC 14 Dex save for half. Targets that fail the save have their movement speed decreased by half and have disadvantage on their attacks rolls until the end of their next turn.
3-Lightning Ray- A blast of electrical energy surges outward from its hand doing 4d6 lighting damage DC 14 save for half. Targets that do not save are stunned until the end of their next turn.
4-Force Ray- A wave of pure magical force blasts outward from its hand doing 2d6 force damage DC 14 dex save for half. Targets that do not save are thrown 20' backwards and knocked prone taking 1d6 damage per 10' thrown if they impact another object or creature.
5-Necrotic Ray- A wave of black necrotic energy blasts outward from its hand doing 4d6 necrotic damage dc 14 dex save for half. Targets that do not save have disadvantage on all saving throws until the end of their next turn.
6-Radiant Blast- A blast of pure radiant energy shoots from its hand and explodes at the targets location. The target and anyone within 5' of the target takes 2d8 radiant damage DC 14 Dex save for half. 

The Arcane Golem has 2 legendary actions per round that can be used to do any of the following things;

Detect (1 action)- Makes a perception check to detect creatures in visual range.

Arcane Blast (2 actions)- As listed above

Move (1 action)- The Arcane golem focuses it' magical energy to shield itself while moving up to half it's movement speed without incurring attacks of opportunity.