Magical reforge. When the A.A.C.'s hitpoints falls to 0 hitpoints, it regains all hitpoints repairing it's body and gaining immunity to the last damage type that made it reach 0 hitpoints, in addition it gains +1 to it's AC and an additional 10ft walking speed, and gets one additional aciton per turn. Magical reforge can be used up to three times keeping the immunities gained this way and any bonuses to it's AC, and on the fourth time it's hitpoints drops to 0, it is destroyed.
The way this works is by the A.A.C.'s body being that of animated metal or other object that builds itself and evolves.
Punch Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 5 (1d6 + 2) bludgeoning damage.
Launch projectile. Ranged Weapon Attack: +4 to hit, range 60/130 ft., one target. Hit: 5 (1d4 + 0) bludgeoning damage.
Description
The A.A.C. or Artificer's accidental creature is a creature gone wrong by an artificer, which combined magical properties, perhaps some alchemical properties and magic, to creature a creature made from metal, clay, wood or any other inorganic material and become animated. The A.A.C. evolves and mends it's own body into something or a shape that would prevent it from taking damage from the thing it's evolving against. An example for this is making it's body rubbery to be immune to bludgeoning damage. Or icy cold to be immune to cold damage, and so forth. Many who encountered this creature lost their lives not because it's powerful, but rather because they were unaware of what the creature it and why it was reviving itself and becoming immune.
Some A.A.C. will have a flying speed (50ft) or even burrow speed (20ft) or swimming speed (40ft) depending on what it's made of and it's shape. It might be intelligent enough to speak and understand languages. The A.A.C. might also be capable of using 1st level spells if imbued with enough magic.
-A.A.C. gives the DM creativity on how the accident happened and such, where as the A.A.C would form into a form with it's own intelligence depending on the magic imbued within it. Usually the A.A.C. would look something like a 3- 6 feet sphere with small legs and arms with no fingers or toes, and a single eye in the middle using a piece of material of whatever it was made of.
Note: This creature is not a goblinoid. I forgot to change that part.
Amazing creation, but I don't think that it would be a CR 1 monster, due to its 57 hit points and AC. But still amazing to use against players.