B.U.D.D.Y.

Bound. The B.U.D.D.Y. is magically bound to an amulet. As long as the guardian and its amulet are on the same plane of existence, the amulet's wearer can telepathically call the guardian to travel to it, and the guardian knows the distance and direction to the amulet. If the guardian is within 15 feet of the amulet's wearer, half of any damage the wearer takes (rounded up) is transferred to the guardian.

Regeneration. The shield guardian regains 5 hit points at the start of each of its turns once it has been out of combat for 1 hour.

Spell Storing. A spellcaster who wears the shield guardian's amulet can cause the guardian to store one spell of 4th level or lower. To do so, the wearer must cast the spell on the guardian. The spell has no effect but is stored within the guardian. When commanded to do so by the wearer or when a situation arises that was predefined by the spellcaster, the guardian casts the stored spell with any parameters set by the original caster, requiring no components. When the spell is cast or a new spell is stored, any previously stored spell is lost.

Configure. The B.U.D.D.Y. can spend a minute to reconfigure into a non-combative mode or vice versa. The difference in each mode is shown below:

Companion: While a companion, the B.U.D.D.Y. can perform more complex tasks, but cannot attack. The B.U.D.D.Y. gains a +10 bonus to all INT, DEX, and CHA checks. While a companion, the B.U.D.D.Y. can do other tasks such as read, write, etc. 

Guardian. While a Guardian, the B.U.D.D.Y. can use its attack actions, but cannot make any ability check other than strength or Wisdom (Perception) checks. It also gains a +10 bonus to said checks. While a guardian, the BUDDY can only speak in simple sentences.

Custom Circuitry. At each dawn, the DM rolls on the Enhancements or Malfunctions Table in Mordekainen's Tome of Foes or on their own custom one.

Multiattack. The guardian makes two fist attacks. One attack can be replaced by a harpoon.

Fist. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 11 (2d6 + 4) bludgeoning damage.

Harpoon. Ranged Weapon Attack: +7 to hit, reach 5 ft. or range 20/60 ft., one target. Hit: 11 (2d6 + 4) piercing damage. If the target is a Huge or smaller creature, it must succeed on a Strength contest against the BUDDY or be pulled up to 20 feet toward the B.U.D.D.Y.

Shield. When a creature makes an attack against the wearer of the B.U.D.D.Y.'s amulet, the guardian grants a +2 bonus to the wearer's AC if the guardian is within 5 feet of the wearer.