Animated safeguard

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

Magic Resistance. The Safeguard has advantage on savingthrows against spells and other magical effects.

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

False Apperance. While the safe remains motionless, it is indistinguishable from a normal safe. 

Locked. If the safe is killed, it's still locked.  The DC for an attempt to pick its lock is 22. 

Safe. The safeguard can store 3 cubic feet of items within it self.

Multiattack The Safeguard makes to Spear Attacks 

Spear Attack Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: # (2d8 + 4) Piercing damage. 

Grapple. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: # (2d6 + 4) Bludgeoning damage. If the attack hits the target makes a DC 15 dexterity save on a failed safe the target is locked within the safe and is restrained and incapacitated. The Safeguard can only contain one creature at a time. As an action it can try to unlock the save (as seen in the locked trait) if it has proficiency with thief's tools or break it open with a DC 25 athletics check. If the Safeguard is opened with an Athletics check the safeguard looses its locked trait and can no longer use the grapple attack. At the start of the Safeguards turn the target locked inside it takes 2d6+4 Bludgeoning damage.

Rod Launcher. RangedWeapon Attack: +8 to hit, range 60/120 ft., one line 5/60. Make an attack role against each target on a hit the targets takes 14(2d8 + 4) Piercing damage. The target makes a Strength Save of 14 or be pined to a wall. The target is Restrained an can free it self with a DC 13 constitution check 

Reaction Name. If a creature misses the Safeguard it cam make one grapple attack  against it.