Amber Vault Guardian

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

Magic Resistance. The Guardian's has advantage on saving throws against spells and other magical effects.

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

Intruders in the Vault. Any creature and its allies that attempt and fail to verify their identity against the Guardian's list of authorised persons is immediately subject to the Guardian's Slow ability with disadvantage on the saving throw. 

Enduring Momentum. The Guardian is immune to the Grappled, Restrained, Incapacitated and Stunned conditions, as well as any effect that would reduce its speed.  

Eternal Watcher. The Guardian has advantage on Perception checks to locate creatures that are inside its designated guardianship. Movement from creatures always provokes opportunity attacks within reach and creatures hit with opportunity attacks have their speed set to 0 for the rest of their turn.  

Multiattack. The Guardian makes two slam attacks.

Slam. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 20 (3d8 + 7) bludgeoning damage.

Crush. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. A creature that is smaller than the Guardian and currently affected by its Slow ability is crushed by both the Guardians hands, dealing 34 (6d8 + 7) bludgeoning damage. 

Slow (Recharge 5–6). The Guardian targets one or more creatures it can see within 30 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.

Summon Lesser Guardians. The Guardian can use its reaction after being reduced to half its hitpoints or less to use its action to animate items in the vault to defend it, similar to the Animate Objects spell.