Armorer (5A)

This is an Artificer Specialization for 5A.

Arcane Armor

[Clarification] You can turn a suit of magical armor into Arcane Armor. Any magic on the suit of armor you use continues to function, but other abilities are determined by your choice of Arcane Armor.
You can add infusions to your Arcane Armor, but when effects overlap only the best effect of the infusion or the armor (including effects from magical armor) applies
Thunder Gauntlets When you use the Attack action with a Thunder Gauntlet on your turn, you can use a bonus action to make an additional attack with your other Thunder Gauntlet, provided you have both hands free.

An artificer who specializes as an Armorer modifies armor to function almost like a second skin. The armor is enhanced to hone the artificer's magic, unleash potent attacks, and generate a formidable defense. The artificer bonds with this armor, becoming one with it even as they experiment with it and refine its magical capabilities.

Source: Tasha's Cauldron of Everything

Subclass Features

Tools of the Trade

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

Armorer Spells

Starting at 3rd level, you always have certain spells prepared after you reach particular levels in this class, as shown in the Armorer Spells table. These spells count as artificer spells for you, but they don't count against the number of artificer spells you prepare.

Armorer Spells Table

**Armorer Spells Table**
Artificer Level	Alchemist Spells
3	Magic Missile, Thunderwave
5	Mirror Image, Shatter
9	Hypnotic Pattern, Lightning Bolt
13	Fire Shield, Greater Invisibilty
17	Passwall, Wall of Force

Arcane Armor

Beginning at 3rd level, your metallurgical pursuits have led to you making armor a conduit for your magic. As an action, you can turn a suit of armor you are wearing into Arcane Armor, provided you have smith's tools in hand.

You gain the following benefits while wearing this armor:

If the armor normally has a Strength requirement, the arcane armor lacks this requirement for you.

You can use the arcane armor as a spellcasting focus for your artificer spells.

The armor attaches to you and can’t be removed against your will. It also expands to cover your entire body, although you can retract or deploy the helmet as a bonus action.

The armor replaces any missing limbs, functioning identically to a body part it is replacing.

The armor continues to be Arcane Armor until you don another suit of armor or you die.

Armor Model

Beginning at 3rd level, you can customize your Arcane Armor. When you do so, choose one of the following armor models: Guardian or Infiltrator. The model you choose gives you special benefits while you wear it.

Each model includes a special weapon. When you attack with that weapon, you can add your Intelligence modifier, instead of Strength or Dexterity, to the attack and damage rolls.

You can change the armor's model whenever you finish a short or long rest, provided you have smith's tools in hand.

Guardian. You design your armor to be in the front line of conflict. It has the following features:

Thunder Gauntlets. Each of the armor's gauntlets counts as a simple melee weapon with the light property while you aren't holding anything in it, and it deals 1d8 thunder damage on a hit. At your option, creature hit by the gauntlet has disadvantage on attack rolls against targets other than you until the start of your next turn, as the armor magically emits a distracting pulse when the creature attacks someone else.

Defensive Field. As a bonus action, you can gain temporary hit points equal to your level in this class plus your Intelligence bonus, replacing any temporary hit points you already have. You lose these temporary hit points if you doff the armor. You can use this bonus action a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.

Infiltrator. You customize your armor for subtle undertakings. It has the following features:

Lightning Launcher. A gemlike node appears on one of your armored fists or on the chest (your choice). It counts as a simple ranged weapon, with a normal range of 90 feet and a long range of 300 feet, and it deals 1d6 lightning damage on a hit. Once on each of your turns when you hit a creature with it, you can deal an extra 1d6 lightning damage to that target.

Powered Steps. Your walking speed increases by 5 feet.

Dampening Field. You have advantage on Dexterity (Stealth) checks. If the armor normally imposes disadvantage on such checks, the advantage and disadvantage cancel each other, as normal.

Extra Attack

Starting at 5th level, you can attack twice, rather than once, whenever you take the Attack action on your turn.

Armor Modifications

At 5th 9th level, you learn how to use your artificer infusions to specially modify your Arcane Armor. That armor now counts as four separate items for the purposes of your Infuse Items feature: armor (the chest piece), boots, helmet, and the armor's special weapon. Each of those items can bear one of your infusions, and the infusions transfer over if you change your armor's model with the Armor Model feature. In addition, the maximum number of items you can infuse at once increases by 2, but those extra items must be part of your Arcane Armor.

Protected Spellcasting

Beginning at 9th level, your concentration cannot break because you take damage.

Perfected Armor

At 15th level, your Arcane Armor gains additional benefits based on its model, as shown below.

Guardian. When a Huge or smaller creature you can see ends its turn within 30 feet of you, you can use your reaction to magically force the creature to make a Strength saving throw against your spell save DC, pulling the creature up to 30 feet toward you to an unoccupied space. If you pull the target to a space within 5 feet of you, you can make a melee weapon attack against it as part of this reaction.

You can use this reaction a number of times equal to your proficiency bonus, and you regain all expended uses of it when you finish a long rest.

Infiltrator. Any creature that takes lightning damage from your Lightning Launcher glimmers with magical light until the start of your next turn. The glimmering creature sheds dim light in a 5-foot radius. The creature gains no benefit from Invisibility and suffers disadvantage on Stealth. Further it has disadvantage on attack rolls against you, as the light jolts it if it attacks you. In addition, the next attack roll against it has advantage, and if that attack hits, the target takes an extra 1d6 lightning damage.

Editor's Notes

A weak subclass, the armorer got a number of upgrades.

The thunder gauntlets became light weapons, allowing you to actually use both of them. Also, the defensive field adds your Int bonus, making it a bit stronger in the early levels.
Armor Modification was moved to level 5. I think this is a core ability of the armorer and cannot wait.
* A new ability, Protected Spellcasting, at level 9. Damage can no longer break your concentration. Artificers are pretty lousy spellcasters, but this really helps to keep their weak spells viable, especially for the tanking artificer.
Perfected Armor/Infiltrator now defeats invisibility. This is an upgrade, but mainly it makes sense.