When I was working on the Knight subclass (now labeled Chevalier), I realized from the feedback that what I really wanted were two separate things. One was the chivalric idea of a Knight (which is what that other thread became), and the other is the heavily armored infantry that this thread is aiming to build.

The idea of this subclass is to have a heavily armored, non-mounted tank that doesn't use magic to bolster its survivability. The image in my mind is the soldier/knight in full plate, wading into battle, leading the charge. I don't want to make anything too powerful, but I certainly don't want a build that is supposed to be a dangerous tank that falls because it folds under the pressure of increased enemy attention. Anyway, here it is. Let me know what you think I need to do better.

Spoiler: Fighter Archetype - Heavy Infantry

Fighter Archetype - Heavy Infantry

You are the foundation upon which the front lines of battle are built. You have the strength of arms that leads the front ranks into the heart of combat as well as the grit to be the bulwark against which the flow of enemy momentum breaks. Formations that you help to organize on the battlefield are renowned for their effectiveness. Being at the forefront of any major battle, heavy infantry are most often known for their melee weapons and heavy armor, though they can make use of any weapon or armor when the need arises like any Fighter. Depending on the weapon they choose to wield, many also carry shields to protect themselves from oncoming hostiles.

Threatening Mark. When you join this martial archetype at 3rd level, you learn to threaten enemies with overwhelming violence in an effort to keep their focus on you. While you are not mounted, when you hit a creature with a melee attack, you also mark the target. Until the end of your next turn, any opportunity attack you make against the marked target has advantage. Opportunity attacks on marked targets do not expend your reaction, but you can't make the attack if anything, such as the incapacitated condition or the shocking grasp spell, is preventing you from taking reactions. You are limited to one opportunity attack per turn.

Armor Modification. Starting at 7th level, you have learned that combat might find you at a moment’s notice. You gain proficiency with smith’s tools, or leatherworker’s tools if you already proficient with smith’s tools.

You have also learned special techniques by which you to modify and don your armor much more quickly than others are normally capable. You can only modify armor for yourself in this way, and it requires you to spend 10 percent of the total price of the armor and at least 8 hours of work in the process.

After you have made the modifications to a suit of armor, when you are not wearing it you can take the normal amount of time it would take you to don the armor to prepare it for quick use. While your armor is prepared in this way, you can don it in a number of rounds determined by its type, as follows. This preparation is interrupted if someone disturbs the elaborate preparation before you make use of it, requiring you to prepare it again. Doffing the armor requires the normal amount of time.

  • Light Armor: 1 round
  • Medium Armor: 2 rounds
  • Heavy Armor: 5 rounds

Finally, if you have modified a shield as described, you can don that shield as a reaction during the first round of combat or as a bonus action at any other time during combat.

Anchor the Line. Starting at 10th level, you can create a formation with your allies in order multiply your weight of arms through defensive and offensive coordination. When you have at least one ally within 5 feet of you and are not mounted, you can use a bonus action to gain 1d8 temporary hit points. You gain the following benefits.
  • You gain 1d8 temporary hit points at the beginning of your turn as long as you have at least one ally within 5 feet of you.
  • You and allies within 5 feet of you reduce any forced movement by 5 feet.
  • Each ally within 5 feet of you can mark 1 target on their turn as if they had the Threatening Mark feature.

This lasts for one minute, or until you start your turn without at least one ally within 5 feet of you. You can use this feature one time. You regain use of this feature when you complete a short or long rest.

Marking Whirlwind. Beginning at 15th level, you are able to threaten all of the enemies around you as you lash out. After you use the Attack action while you are not mounted, you can use a bonus action to cause any number of creatures you choose within 5 feet of you to make a Constitution saving throw with a DC of 8 + your proficiency modifier + your Strength or Dexterity modifier (your choice). On a failed save, a creature takes damage equal to your Strength or Dexterity modifier (your choice) and is marked. On a success, it does not take the damage but is still marked.

Iron Anchor. Starting at 18th level, you can use your Anchor the Line feature 2 times before you must complete a short or long rest. Additionally, while Anchor the Line is active, you have resistance to bludgeoning, piercing, and slashing damage.