Adamantine Spirit. The Adamantine Guardian's form cannot be changed by magic, and is immune to all spells that turn it into another creature. 

Soul of Spell Storing. The Adamantine Guard can store one spell up to 5th level inside its chest. The spell will remain stored until used, or until the Guardian is felled in battle. At which point the spell is waisted. The spell can be cast as an action from the Guardian regardless of the spells casting time, or a bonus action or reaction if permitted by the spell. The stored spell can be changed once per day, and new spells can be stored twice per day. 

Multi-Attack. The Adamantine Guard makes two Longsword attacks, or one Bolt attack

Longsword. Melee Weapon Attack: +7 to hit, reach 5 ft., 1 target. Hit: 7 (1d10 + 5) [slashing] damage. 

Action Ranged Attack. RangedWeapon Attack: +# to hit, range 20/60 ft., 1 target. Hit: 12 (2d6 + 2) [piercing] + (1d8) [fire] damage.

Mechanical Jump. As a bonus action, the Guardian can add 10 feet to its jumping distance. 

Guardian of the Boon. As a reaction, the guardian can move up to half its movement speed to protect the wielder of the boon that it protects. When it reaches the creature it is bound to protect, it throws itself in front of the weapon or spell attack, adding 1d6 to the AC of the protected creature. This has no effect on Spell Saving throws.