Bone Dragon Golem [Credit to Fermin Caballero (MrRhexx)]

Magic Immunity. The golem is immune to all spells, spell-like abilities, and supernatural effects, except by those that originate from an artifact or deity.

Critical Immunity. Critical hits against the golem are treated as normal hits.

Magic Weapons. The golems' weapon attacks are considered magical.

Unusual Nature. The golem doesn’t require air, food, drink, or sleep.

Multiattack. The golem can use its frightful presence. It then  makes three attacks, one with its bite and two with its claws.

Bite. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 15 (2d10 + 4) piercing damage.

Claws. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 11 (2d6 + 4) slashing damage.

Tail. Melee Weapon Attack: +8 to hit, reach 15 ft., one target. Hit: 13 (2d8 + 4) piercing damage.

Frightful Presence. Each creature of the golem's choice that is within 120 feet of the golem and aware of it must succeed on a DC 16 Wisdom saving throw or become frightened for 1 minute. A frightened creature can repeat the saving throw at the end of each its turns. On a successful save, the effect ends on the target. If a creature's saving throw is successful or the frightened effect ends for it, the creature is immune to the golem's Frightful Presence for the next 24 hours.

The dragon 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 dragon regains spent legendary actions at the start of its turn.

Detect. The golem makes a Wisdom (Perception) check.

Tail Attack. The golem makes a tail attack.

Wing Attack (Costs 2 Actions). The golem beats its wings. Each creature within 10 feet of the dragon must succeed on a DC 16 Dexterity saving throw or take 11 (2d6 + 4) bludgeoning damage and be knocked prone.