Aegis Engine

Integrated Threat Assessment: The Aegis Engine uses Constitution, not Wisdom, to calculate its Perception skill bonus. Additionally, if an attack against itself or an ally within 5ft fails, the Aegis Engine can attack the creature as a reaction.

Motive Engine: Given its arcanomechanical nature, the Aegis Engine can be affected by healing spells, but the hits points restored are reduced by half when targeting it. Additionally, the Mending cantrip can be used on a Aegis Engine that has more than half its maximum hit points, and restores hit points equal to 1d8 + the caster's spellcasting modifier.

Motive Engines cannot speak by default, but have a variable number of Language slots that can be fitted with Enhancement Drives. The knowledge of words and rudimentary sentences takes one slot, and an additional slot for the Motive Engine to be able to say more complex sentences.

Multiattack. The Aegis Engine makes one great hammer attack and one shield bash.

Great Hammer. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 8 (1d10 + 3) bludgeoning damage.

Shield Bash. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 7 (1d4 + 3) bludgeoning damage. Creatures hit by this attack must succeed on a DC13 Constitution Saving Throw or suffer disadvantage on their next attack.

Core Overcharge (Recharge 3 turns): The Aegis Engine activates its emergency power supply. Until the start of its next turn, it gains a +2 bonus to its hit rolls, increases the range of Selfless Protocol by 10ft, the Shield Bash DC increases to 15 and if the creature fails they become stunned until the end of their next turn.

Selfless Protocol: When an allied creature within 10ft is targeted by a melee attack, the Aegis Engine can use its reaction to intercept it. It will move to the creature's location and, if safe, move it 5ft behind it, forcing the attack to target it instead. It will then lose as much movement speed as the distance moved until the end of its next turn.
If the attacking creature moves in its turn towards the ally while within the Aegis Engine's engagement area, the Aegis Engine can immediately make a melee attack against it.