Bell Golem, Artifact Guardian

Bludgeoning Reflection. Whenever the golem is subjected to bludgeoning damage, it takes no damage and instead reflects damage equal to the bludgeoning damage dealt to all creatures within a 10ft radius centered on the Bell 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.

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

Legendary Resistance (3/Day). If the Bell Golem fails a saving throw, it can choose to succeed instead.

Adamantine Armor. The Bell Golem cannot suffer a critical hit.

Multiattack. The golem makes three melee attacks, as well as casting one spell or using its Toll of The Bell ability.

Slam. Melee Weapon Attack: +13 to hit, reach 10 ft., one target. Hit: 20 (3d8 + 7) bludgeoning damage.

Aurelios, The Time Dagger. Melee Weapon Attack: +13 to hit, reach 5 ft., one target. Hit: 19 (2d10 + 9) force damage.

Toll of the Bell (Recharge 5-6). The golem rings its own bell. Each creature within a 20ft radius must make a DC 19 Constitution saving throw, taking 40 (9d8) force damage on a failed save, or half as much damage on a successful one.

Additionally, any creature who fails falls prone, and is stunned until the end of their next turn.

Spellcasting. The Bell Golem casts one of the following spells, requiring no spell components and using Intelligence as the spellcasting ability:

3/day each: shield (self only), misty step (self only)

Shell Up. When targeted with an attack, the Bell Golem can retreat into itself. When it does so, it gets a +5 bonus to it's AC, it's movement speed becomes 0, and it cannot take any actions of any kind until it comes out of it's shell at the beginning of it's next turn.

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

Detect. The Bell Golem makes a Wisdom (Perception) check.

Slam Attack. The Bell Golem makes a Slam attack.

Shake The Earth (Costs 2 Actions). The Bell Golem tucks into itself and begins vibrating quickly, causing the area around it in a 20ft radius to become Difficult Terrain. Each creature within 20ft must make a DC 17 Constitution saving throw. Any creature who fails falls prone, and is stunned until the end of their next turn.