Commodore Heinz' Mech

Electricity Recapture. Whenever the golem is subjected to Lightening damage, it regains a number of Hit Points equal to the Lightening damage dealt.

Immutable Form. The Mech can’t shape-shift.

Legendary Resistance (3/day). The Mech can choose to succeed on a saving throw it would otherwise fail.

Storage Flywheel. The Mech features a Flywheel for storing energy in order to fire the Gatling gun, the Flywheel Speed Level controls the damage the Gatling Gun Deals.
Lvl 1. 1d10 Expends 3 bullets.
Lvl 2. 2d10 Expends 6 bullets.
Lvl 3. 3d10 Expends 9 bullets.
Lvl 4. 4d10 Expends 12 bullets.
Lvl 5. 5d10 Expends 15 bullets.
Lvl 6. 6d10 Expends 18 bullets.
Lvl 7. 7d10 Expends 21 bullets.

Pin Down DC.

Lvl 2. Failure, unable to fire fast enough. Expend 3 bullets.
Lvl 3. Success, you fire enough to fill a 5ft cube(One tile) with lead. Expends 10 bullets.
Lvl 4. Success, you fire enough to fill 2 5ft cubes (2 tiles) with lead Expends 20 bullets.
Lvl 5. Success, you fire enough to fill 3 5ft cubes (3 tiles) with lead Expends 30 bullets.
Lvl 6. Success, you fire enough to fill 4 5ft cubes (4 tiles) with lead Expends 40 bullets.
Lvl 7. Success, you fire enough to fill 5 5ft cubes (5 tiles) with lead Expends 50 bullets.

Expanded Accles Drum. Holds 208 rounds and can be reloaded with an Action, if insufficient ammo is available the max lethality is capped at less than or equal to what is left. 

Automatic Reload. Automatically reloads over the course of a round. 

Multiattack. The golem makes three attacks, using Arm Crush, Flammenwerfer or Gatling gun in any combination.

Arm Crush. Melee Attack Roll: +12, reach 10 ft. Hit: 20 (3d8 + 7) Bludgeoning damage 

Flammenwerfer. Ranged Attack Roll: +10, range 60 ft. Hit: 36 (8d8) Fire damage.

Electric Motor Windup. Increase the Flywheel Level by two.

Gatling Gun attack. Make a Gatling gun attack with a +12 to hit, damage is dependent on the Flywheel storage level. Additionally add a +7 to damage delt.

Pin Down. Enemies are temporarily pinned down, consult the Pin Down table and flywheel level for effects.

Electric Motor. Increase the Flywheel Level by one.

Armor Configuration. Each configuration lasts for a round, and has a single Charge

Ablative Armor. Grants 2d10 Temporary hit points for one round.
Lightening Charged. Whenever a creature within 5 ft of the mech hits it with a melee attack, the charged Armor arcs with electricity. The attacker takes 3d8 Lightening damage. Lasts for one round.
Elementally Grounded. Grants Resistance to a random damage type for one round.
Absorptive Armor. Over the course of one round, half all damage taken is also stored for the first attack taken after the round is over. If the attack misses the damage is lost, and the damage type takes on the type of the attack taken.

Steam Shunt (3 Charges, Recharge 5-6). The Mech Shunts 15ft. in a straight line in any direction. Any Creature caught in the line must make a DC 17 Dexterity saving throw. Failure takes 4d10 Bludgeoning damage and half as much on a successful save. Steam Shunt also grants advantage on Dexterity Throws and a +5 bonus to AC. 

 Parry. The Mech can parry a single melee attack, increasing its AC by +3 against that attack.

Soak. The Mech can use an attack before its next turn to reduce an incoming attacks damage by half. That attack reduces the total to 2 during that next turn.

The Mech can take 3 Legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The dragon regains spent legendary actions at the start of its turn.

Electric Motor (Costs 1 Action). Increase the Flywheel Level by one.

Unleash Lead (Costs 2 Actions). The Mech makes a Gatling Gun attack.

Flame Attack (Costs 1 Action). The Mech makes a Flammenwerfer attack.

Switch Configuration(Costs 1 Action). The Mech switches armor configuration.

Phase 1: Good Mech Condition
Phase 2: Refill to 200 hit points(or 150, depending on player success), Reduce AC to 15, Reset Shunt Charges and double the total number of charges to 6. Randomize Armor Configuration every Round and ignore charge limits.
Phase 3: Once the Mech reaches 50 hitpoints during phase two, it reaches Critical Condition and after two rounds its steam engine detonates. Showering any creatures within 30ft. are hit with shrapnel and must make a Dexterity Saving Throw. On a failed save, the creature takes 10d8 damage and is knocked prone. On a Success the creature takes half damage and is not knocked prone. Heinz is automatically ejected with an emergency ejector launching him 60ft in the air with him flying on mechanical wings. He can choose to Eject early using a bonus action, action or legendary action.

His new stats are as follows.

AC - 17
Fly Spd. 120ft.
Multiattack with 2 attacks.
Mare's Leg, Capacity 6 rnds. Dual Wielding one in each hand. +10 to hit. 1d8+10 piercing damage.
Hp (100 or 50) 
Wings last for 3 rounds before an action must be spent recharging them.
Bonus action can be used to attack once or reload 1 cartridge in each gun.
Str - 14
Dex - 18
Con - 16
Int - 20
Wis - 16
Cha - 16
No legendary Actions.