Clockwork Aberration

Clockwork Encasement. The creature within the machine is a somewhat shapeless mass, both protected and given concrete manipulators by its armor. The clockwork armor has a variety of manipulators that the Clockwork Aberration can use to attack or to interact with objects outside the armor. When the clockwork aberration is reduced to 0 hit points, its clockwork armor breaks and the aberration exits it. Once out of its armor, the creature's pulpy mass no longer receives the benefits of its Damage or Condition immunities except for psychic and prone, and its AC becomes 12 and it has 27 (5d10 + 10) hit points remaining. It also has a movement speed of 20 feet and a Strength of 9 (-1). It has no attack actions but it can cast spells. The aberration's body can form eyes, mouths, and grabbing appendages. It can pick up objects, but not use them as weapons. The aberration can enter and exit its armor as a bonus action.

Immutable Form. The clockwork aberration's armor is immune to any spell or effect that would alter its form, as is the creature that controls it as long as it remains within the armor.

Spellcasting. The clockwork aberration innate spellcasting ability is Intelligence (spell save DC 14, +6 to hit with spell attacks). The clockwork aberration can innately cast the following spells, requiring no material components:
-At will: firebolt (2d10), telekinesis 

Multiattack. The Clockwork Aberration makes three melee attacks. It can cast one at-will spell in place of two melee attacks.

Whirring Blades. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 8 (2d4 + 3) slashing damage. 

Pronged Scepter. Ranged Weapon Attack: +5 to hit, reach 10 ft., one target. Hit: 6 (1d6 + 3) piercing damage.

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