Basically, this makes you the Tony Stark of D&D. If this is unbalanced, please tell me how to fix it.
Mechanist, Artificer Subtype
Iron Body: Beginning at first level, you calculate your AC as 14 + your proficiency bonus.
Modifications: Also beginning at 1st level, you further mechanize and/or augment your physical form for different purposes and with different effects. Choose one of the following minor modifications. You choose another at 3rd, 9th, and 14th.
You can attempt to change your modifications after a long rest, doing so requires a tinkerer’s tools (intelligence) check, the DC for this check is equal to 13 plus twice the number of modifications you are attempting to change. On a failed check, you are unsuccessful in your efforts and must make an additional check to attempt to fix your original modifications. The DC to fix a modification is 15, if this check is also failed, you no longer benefit from it as it is non-functional. You may repeat the repair check after a short rest.
You gain advantage on stealth checks when you use half or less of your movement speed, in addition you may roll a stealth check and hide without any cover (no action required). Can be chosen a maximum of one time.
Doubles the normal range for attack rolls with ranged weapons (must have the ammunition property), and the long range is doubled. Can be chosen a maximum of one time.
You can now breath underwater from your mechanical gills, also you gain a swim speed equal to half your base movement speed thanks to retractable flippers. Can be chosen a maximum of one time.
Auditory Tracking Unit
Increases Blindsight by 15 feet, relies on your ability to hear. Can be chosen a maximum of two times.
You gain a +1 to your AC. Can be chosen a maximum of two times.
Your superior footing grants you advantage on any save or check against being knocked prone. In addition, difficult terrain doesn’t cost you any extra movement. Can be chosen a maximum of one time.
Once per long rest when you are reduced to 0 HP but not killed outright, on your next turn electricity surges through your body and jolts you back to consciousness; instead of rolling for a death saving throw, you automatically gain 1 HP. Can be chosen a maximum of one time.
As an action you can now release a 20-foot by 5-foot line of flames in front of you. Each creature in the line must make a Dexterity saving throw. A creature takes 2d4 + your intelligence modifier fire damage on a failed save, or half as much damage on a successful one. The fire ignites any flammable objects in the area that aren’t being worn or carried. You have two uses of this ability, all expended uses recharge on a short or long rest. Can be chosen a maximum of one time.
Your extreme grip imposes disadvantage on any check an enemy is using to attempt to break free of or escape from your grapples. You also gain a climb speed equal to half your base movement speed. Can be chosen a maximum of one time.
Increases darkvision by 30 feet. Can be chosen a maximum of two times.
You affix a sparking device behind a lens on a part of your body, when activated it casts bright light in a 30-foot cone and dim light for an additional 30 feet. As an action, you can lower the intensity of the spark, reducing the light to dim light in a 5-foot cone. As an additional action, once per short rest, you can greatly intensify the spark for a moment, any creature that can see you in a 30-foot cone in front of you must make a Constitution saving throw. On a failed save, a creature is blinded until the start of your next turn. On a success the creature is unaffected.
You gain advantage on all charisma-based checks when interacting with creatures that are within 30 feet of you and can see you. Mutually exclusive with Heat Vision. Can only be chosen a maximum of one time.
Your augmented locomotion increases your speed by 10 feet. Can be chosen a maximum of two times. Major Modifications: At 18th level, you choose one of the following modifications. This cannot be changed.
You implant yourself with the Huge Adrenaline Release Mechanism. As a bonus action you may trigger this mechanism for a specialized effect. The mechanism comes in two varieties, you may choose only one.
H.A.R.M. Ω When you are wielding a ranged weapon this allows you as your action this turn to attack any number of creatures within a 15-foot radius of a point you can see within your weapons range. You must have ammunition for each target, as normal, you make a separate attack roll for each target.
H.A.R.M. ß When you are wielding a melee weapon you can add half your Intelligence modifier (rounded up) to all your attack rolls this turn, in addition, you can use your action to move up to half your speed and make a melee attack against any number of creatures that came within 5 feet of you during this movement. You must make a separate attack roll for each target, and this movement provokes attacks of opportunity as normal. Whichever variety you choose, at the end of your turn, until the beginning of your next turn, enemies have advantage on attack rolls made against you and you have disadvantage on saving throws you make as you are briefly worn out from the sheer intensity of your efforts.
You graft layers of metallic plates beneath your skin, as a result you gain +2 to your AC and develop resistance to cold damage and fire damage.
Augmented Targeting System
You surgically implant a series of enchanted retractable lenses to your skull that allow you to more accurately and precisely identify your enemy’s weaknesses. Your attacks now score a critical hit on a roll of 19 or 20.
You replace the tendons in your body with enchanted metallic strands and as a result, whenever you score a critical hit with a weapon attack, you may perform an additional attack as part of your attack action with that weapon. This effect can only trigger from your standard attack actions and not from the bonus attacks granted by this ability.