Engineer

Engineers specialize in the creation of mechanical suits to assist them in their tasks, whether it's big or small. They can build large robotic bodies that they can then pilot in order to gain extra leverage on the battlefield against their non-mechanical enemies. Some even go as far as to enhance their own bodies with upgrades similar to those granted by their "mech" suits.

The art of the engineer is a fairly new practice, so not many people follow it, but having one of these rare diamonds in your party is always a boon.

Tool Proficiency

When you adopt this specialization at 3rd level, you gain proficiency with smith's tools. If you already have this proficiency, you gain proficiency with one other type of artisan's tools of your choice.

Mech Suit

At 3rd level, you gain the ability to create a Large vehicle (land) to assist you in a given situation. The vehicle, henceforth referred to as a "mech" or "mech suit", shares most of your statistics, with a few exceptions and changes noted below. To create one, you must have access to smith's tools, and a quantity of the metal you wish to make it from listed in the mech's description and a few other miscellaneous parts for it's more mechanical components. The value of these parts are measured in gold pieces (gp). It takes 1d6 + 3 hours to finish building a mech (unless specified otherwise, either by the mech's description or your DM) with the materials readily available to you, and a mech counts as one of your infused items until it is destroyed. The metal you choose determines the benefits you gain from your mech, as described below:

Iron Mech. Forged from iron, this mech is the most common one found amongst engineers. You must have at least 200 gp worth of iron and other miscellaneous parts to build this mech. Your DM may let you substitute iron for similar metals, such as silver or copper, to build this mech. You gain the following benefits while wearing it:
- You gain a +3 bonus to your AC.
- You have advantage on Strength checks, Strength saving throws, and Strength-based attack rolls.
- Your movement speed decreases by 10 feet.
- You have disadvantage on Dexterity (Stealth) checks, and have a -10 penalty to them.
The Iron Mech has 100 hit points.

Gold Mech. This mech is constructed from gold, and meant to be more flashy than practical. However, it is also the mech of choice for those who work in construction, as it was designed with the intention to work on such projects. You must have 1,000 gp worth of gold and other miscellaneous parts to build this mech. You may not use the gold coins as a substitute. You gain the following benefits while wearing it:
- You gain a +2 bonus to your AC.
- Climbing costs you no extra movement.
- You can cast the mold earth cantrip while wearing the mech. It counts as an artificer spell for you while you are in the mech.
- You have disadvantage on Dexterity (Stealth) checks, and have a -10 penalty to them.
The Gold Mech has 60 hit points.

Mithral Mech. Designed to assist agile swordfighters and warriors, the mithral mech is made to be light and easy to control. You must have 800 gp worth of mithral and other miscellaneous parts to build this mech. You gain the following benefits while wearing it:
- You gain a +2 bonus to your Dexterity score.
- You can use Dexterity in place of Strength for weapon attacks that normally require Strength. 
- You have advantage on Dexterity saving throws against spells and other effects that require Dexterity saving throws. In addition, when an ally of yours is targetted by an effect that allows it to make a Dexterity saving throw for half damage, you can use your reaction to grant that ally advantage on the saving throw. The ally must be within 30 feet of you and you must be able to see the ally when this happens in order to use this feature.
The Mithral Mech has 120 hit points.

Adamantine Mech. Adamantine mechs are used by engineers who seek to absolutely dominate the battlefield. They are extremely difficult to construct, and take 1d6 + 3 weeks to complete, rather than the typical 1d6 + 3 hours required by other mechs. In addition, due to the rarity of adamantine and how expensive it is, very few engineers actually get the chance to create one. You must have 2,000 gp worth of adamantine and other miscellaneous parts to build this mech. You gain the following benefits while wearing it:
- Any critical hit against the mech becomes a normal hit.
- You gain advantage on Strength checks, Strength-based attack rolls, and Strength saving throws. You also have advantage on Constitution saving throws. Additionally, you gain a +2 bonus to your Strength score.
- Whenever you hit a creature with an unarmed strike, it counts as a critical hit.
- Your movement speed is halved. In addition, you cannot climb, swim, or jump while in the mech suit.
- You have disadvantage on Dexterity saving throws, Dexterity-based attack rolls, and Dexterity checks. You also have a -10 penalty to Dexterity (Stealth) checks.
The Adamantine Mech has 200 hit points.

A mech has immunity to poison and psychic damage. In addition, the mech is immune to the blinded, deafened, charmed, exhaustion, frightened, petrified, poisoned, and unconscious conditions. A mech is unable to regain hit points unless repaired with tinker's tools (see "Tool Descriptions" in chapter 2 of Xanathar's Guide to Everything). Whenever a creature attempts to target you with an attack, spell, or other effect while you are operating your mech, the effect instead targets the mech.
All mechs have an unarmed strike attack option that you may use in place of a weapon attack while you wear it. You use the mech's arm is place of your own to make this unarmed strike. You are proficient with the attack, and add your Strength modifier to it's attack and damage rolls. On a hit, a creature takes 1d10 bludgeoning damage. All mechs are also capable of wielding weapons, and follow the regular rules for holding them as if you were wielding the weapon.

Variant: Foregoing Materials

Your DM may allow you to forgo the need to buy components at the expense of spell slots, infusions, or other resources they find appropriate to what you want to build. This can be explained as using magic to create you desired mech suit seemingly from thin air. A mech suit created in this way vanishes after you take a long rest.

Once a mech is reduced to 0 hit points, it is destroyed and you lose it's benefits if you were wearing it at the time. A destroyed mech explodes, and if you are wearing it when it is destroyed, you take 4d6 fire damage from the explosion. In addition, every creature within 10 feet of you must succeed on a DC 12 Dexterity saving throw. A creature takes 4d6 fire damage on a failed save, or half as much damage on a successful one.

Improved Mech

Starting at 5th level, you can spend an extra 100 gp on construction materials for your mech. Doing so allows you to improve it's melee attacks. When you make an attack using the mech's unarmed strike, the damage dealt by it increases by 1d10. Additionally, when you make a melee attack using a weapon the mech is wielding, that attack deals an extra 1d6 damage of it's type. This benefit is lost if your mech is destroyed.

If you are using the Foregoing Materials rule, you can instead expend a 1st, 2nd, 3rd, 4th, or 5th level spell slot. The additional damage increases by 1d6 per spell slot level, to a maximum of 5d6. This benefit is lost when you finish a long rest or when your mech is destroyed.

Unfriendly Fire

At 9th level, whenever a mech you are operating is destroyed, you and your allies are magically shielded from the explosion, and take no damage from it. In addition to this, creatures hostile to you have disadvantage on their saving throw against the explosion. 

Mechanical Master

At 15th level, you have mastered your ability to create mech suits that aid you in combat:

• The atttacks from your mechs count as magical for the purpose of overcoming resistance and immunity to nonmagical damage. This effect applies even if the mech is wielding a nonmagical weapon.
• Whenever your mech hits a target with an attack, the target takes an extra 1d10 of the appropriate damage type.
• If a spell you cast requires a costly component, you may use a mech you create to replace that component, assuming the mech has an equal or greater value than the item required. When a mech is used in this way, it is destroyed, but it does not explode. Instead, it simply vanishes.