Steam knight

As new technology is made, applications for that tech that were impossible before, become possible. The steam knight is one of those applications. Large humanoid creations of brass and steal, they are a fusion of steam powered pistons, overlapping armor plates, and arcane furnaces. The steam knight runs fearlessly into battle, towering over its comrades, to wreak havoc among enemy lines using weapons too heavy to be wielded by most other humanoid races.

first attempt at home brewing a subclass so any criticism is welcome. I also need someone more creative than me to write the descriptions for this subclass

Vehicle Proficiency

3rd-level Steam Knight feature

You gain proficiency with Vehicles (land). If you already have this proficiency, you gain proficiency with one other type of artisan’s tools of your choice.

Steam Knight Spells

3rd-level Steam Knight feature

You always have certain spells prepared after you reach particular levels in this class, as shown in the Steam Knight Spells table. These spells count as artificer spells for you, but they don’t count against the number of artificer spells you prepare.

Steam Knight Spells

Artificer Level	Spell
3rd	thunderwave, shield
5th	branding smite, heat metal
9th	melf's minute meteors, erupting earth
13th	fabricate, wall of fire
17th	creation, wall of stone

Combat armor

3rd-level Steam Knight feature

Your combat training and your experiments with magic have paid off in two ways:

• You gain proficiency with martial weapons.
• When you attack with a weapon while wearing your steam armor, you can use your Intelligence modifier, instead of Strength or Dexterity modifier, for the attack and damage rolls.

Steam armor

3rd level Steam Knight feature

You have built yourself a suit of heavy armor powered by steam and magic. At 3rd level, you can spend one week to build a suit of steam armor, provided you have the right materials. To use this armor, you must be attuned to it. 

While wearing your steam armor:

• your size increases to large
• you cannot cast spells that target anyone but self while wearing your steam armor
• your steam armor can be used as an arcane focus
• your armor class is equal to 15 + your intelligence modifier
• you can use your intelligence instead of strength when making a strength check and when determining carrying capacity

Mobile bastion

3rd-level Steam knight feature

The machine that steam knights pilot is comparable to a walking tank, providing many layers of defense before the pilot takes any true damage.

• Your steam armor has a number of hit points equal to 5 times your level in artificer + your intelligence modifier
• The pilot will not take any damage except for psychic and lightning damage until this hit point pool has been reduced to 0
• you have resistance to poison and fire damage until the armors hit points are reduced to 0
• these hit points can only be recovered by taking a long rest or half can be recovered by taking a short rest
• you still gain all of the benefits of wearing your steam armor even after these hit points have been reduced to 0

Extra Attack

5th-level Steam knight feature

You can attack twice, rather than once, whenever you take the Attack action on your turn.

improved machinery

9th-level Steam knight feature

You can, as a bonus action, restore 3d4 hit points back for your steam armor. You can use this a number of times equal to your Intelligence modifier (minimum of once), but you can do so no more than once on a turn. You regain all expended uses when you finish a long rest.

Siege weapons

5th-level Steam knight feature

Swords taller than a grown man, hammers bigger than a Goliaths torso, and axes with blades the size of a taverns table. The weapons wielded by steam knights are massive and heavy, often used to smash down the gates of castles.

over the course of a long rest, you can use smiths tools or tinker tools to build a siege weapon. Siege weapons are large sized martial weapons that do an additional d4 of damage per hit. most siege weapons cannot be used by medium sized creatures, the exception being siege short swords which count as a great sword when used by a medium creature.

conductive armor

9th level Steam Knight feature

at 9th level, you can cast spells at targets other than self while wearing your armor.

expert mechanic

15th-level Steam Knight feature

• your steam armor gains +2 armor class
• your improved machinery increases to 6d4
• you gain advantage on strength ability checks while wearing your steam armor