Can you lower your AC on purpose?

Question

For roleplaying reasons I would like to make a NPC appear weaker than it actually is. When the players first fight it, it should seem to have a very low AC and miss many attacks.

Is this possible in RAW or in RAI? Failing a saving throw on purpose seems to be RAI:

On March 10, 2016, Jeremy Crawford tweeted, "No rule lets you opt to fail a save. As DM, I might allow it, assuming you aren't incapacitated or dominated." Mike Mearls also said that he would allow it (as a DM).

Can you choose to fail a saving throw?

Can I choose to let a punch hit me, or to attack weaker or slower than 100% of my skills would allow?

Answer 1

Technically, you can't do this

There are not rules that support being able to choose to be hit or to choose to miss with an attack. In fact, there are even features that only activate when you are hit or when you miss and so a character could activate them intentionally which is otherwise not possible and potentially imbalancing in some cases (I can't imagine it making that much of a problem, but I haven't examined every case).

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Technically, you can (and should) do this anyway

You are the GM, you can do what you want. If this NPC wants to allow attacks to hit them and wants to either attack with less strength than usual or wants to purposefully miss with their attacks, you can just make that happen.

Theoretically, you could have them make some sort of ability check (maybe performance) to see whether their plan comes across as if they are genuinely trying in the combat, but if this is all for the narrative anyway there's really no reason. Just let it happen if you feel it will improve the player experience, you aren't bound to the rules and I would, in fact, encourage bending them or flat out ignoring them when it lets you build the narrative for your players.

Answer 2

Look Away!

In the PHB Combat Section, "Making an Attack" explains that...

When you attack a target that you can't see, you have disadvantage on the attack roll... When a creature can't see you, you have advantage on attack rolls against it.

RAW, your NPC could deliberately close their eyes or look away when attacking or being attacked, making it more difficult for them to hit and easier for them to be hit. In your comment you say that you don't want to give your players advantage to hit the NPC as they would become suspicious. If you play on a VTT and have advantage/disadvantage automatically displayed, you can consult it without the players being aware that you are using it. If not, you can simply apply a flat +/-5 adjustment to the rolls instead without informing the players of the bonus or penalty.

I would allow players to notice this behavior (with a contested Insight vs. the NPC's Performance or Deception) if they asked why the NPC was so easy to hit or why it was having such a hard time hitting them.

However, as the other answers have stated, you needn't feel constrained by RAW as a DM. This NPC is your NPC. If you need them to operate differently for plot reasons, that is entirely within your purview.

Answer 3

As the DM, you can do this if you want.

As written, there is no rule that states you can do this. But you’re the DM, and you can design your bad guys however you want. There are several spells that raise AC, like mage armor and shield of faith, but as the DM, you can just give your bad guy a feature that raises their AC at the cost of an action or bonus action, or whatever you like. There doesn’t need to be a rule or feature already written for this. Just raise or lower the bad guy’s AC as desired for the particular fight.

Answer 4

AC is not fully under your control

Besides your choice or armor and buffs, of course...

Player's Handbook, page 14

Your Armor Class (AC) represents how well your character avoids being wounded in battle. Things that contributes to your AC includes the armor you wear, the shield you carry and your Dexterity modifier.

This implies your AC is the sum of your armors plus your agility (Dexterity) to avoid being hit.

However, it is not fully under your control, as we can see in the Unconscious condition.

Unconscious Condition, Player's Handbook, page 292

• An unconscious creature is incapacitated (see the condition), can’t move or speak, and is unaware of its surroundings.
• The creature drops whatever it’s holding and falls prone.
• The creature automatically fails Strength and Dexterity Saving Throws.
• Attack Rolls against the creature have advantage.
• Any Attack that hits the creature is a critical hit if the attacker is within 5 feet of the creature.

So, when you attack an unconscious target, you get advantage and critical hit if you meet the requirements, but even so, you still have to beat the target AC. Even the dexterity bonus will apply under this condition.

From a DM's perspective

You are free to do as you like. Think of your NPC as any other foe. When the DM is designing it's monsters and villains, they can have whatever trait, attribute or power they want.

About house rules

You could make characters have control of their Dexterity bonuses in their AC. So, a character with a leather armor and +3 Dexterity bonus could choose to lower the AC to no less than 11.

Answer 5

Your NPC is more than one NPC

A.k.a the multi-phase boss fight

Build more than one stat block for the character. This allows you to make honest and consistent rolls for the current situation. The rest is just the usual descriptions and roleplay.

There's already precedent in the DnD canon: there are legends that Bahamut, the Platinum Dragon, sometimes explores the mortal plane on foot, pretending to be an old man in plain garb accompanied by seven canaries.

The nice thing about NPCs is that they don't have to play by the same rules as player characters. There's a whole host of tropes about kings, princesses, legendary warriors and the like hidden among the common folk, sometimes for years. You can create multiple stat blocks, just like for multi-phase bosses, that represent how much the character is holding back. This represents a practiced persona, not something attempted on short notice, which is why its consistent.

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Vash is the village pushover. He's always losing wrestling matches with the kids. He's a nice enough guy and he's always helpful to anyone who needs it, but he really couldn't win against those kids, according to the stats here labeled 'Vash, Village Pushover'. AC 9, HP 5, Attack -1. He stood no chance once those ruffians roll into town. A single shot took him out while he defended the lady who runs the restaurant. Strange that he's still breathing, though.

Until he's given no choice but to fight. Now he's 'Vash, Mysterious Gunman'. This stat block says AC 15, HP 60, Attack +7 even Acrobatics Expertise. Too much for some random bandits to handle safely, but surely within the normal realm or possibility, right?

Then the strange happens. A mysterious heavy hitter is leveling buildings, and our pushover is almost not recognizable. 'Vash the Stampede' has AC 22, HP 300, Speed 50. It's a good thing that this NPC has his own story that only temporarily intersects with our player characters. Either that or events resolve so that Vash can go back to leading a peaceful life losing wrestling matches against kids. At least nobody died.

Answer 6

You could go Rock Lee style and secretly encumber the enemy with hidden weights beyond their carrying capacity. This will give them a disadvantage on attack rolls by RAW and reduce their speed. Giving them ring mail without proficiency in heavy armor will also remove their dex bonus and the lowest base ac of 14 for heavy armor and similar effects to being encumbered. A high level dexterous character relying on unarmored defense could cause their optimal AC to drop substantially in this way.

Wielding a strength based weapon when they’re high on dex but low on strength could also mask their optimal modifiers.

Lastly the spell slow will reduce AC by 2.

Answer 7

Ignore defence while fighting is a class feature of Barbarians (making Reckless attacks, giving opponents advantage). Your enemies can tell you're doing this.

It takes training to do that in a real fight when people are really trying to kill you; the instinct for self-defence is pretty strong, I'd think. (That's why only barbarians can do this, not any class¹). Especially against physical weapons that you instinctively know are going to hurt. (Less so for a spell touch attack, perhaps, if you haven't been hurt by that spellcaster or that spell before.) I don't have a suggestion for how to mechanically figure out whether a non-Barbarian character is capable of letting themselves be hit more easily.

Note 1: You could argue that anyone can ignore defence, but only Barbarians can gain advantage on their own attacks from doing so. And that the rules wouldn't bother to list something you can do that's purely detrimental to yourself. Still, ignoring defence in real combat takes some serious mental fortitude if you can still see the blows coming.

As a DM, you're free to make up whatever you want, but hopefully it should be consistent with that picture of how combat works.

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Other methods of granting advantage to opponents (like intentionally not looking) are likely to be hard to disguise. In-game, characters will know what it's like to fight someone with their weapon of choice; what sort of defensive reactions are normal when someone sees a swing or thrust coming. If that doesn't happen when they're not flanking or something, so the enemy should have been able to see the blow coming, it will be surprising and probably noticeable if there's consistently no dodge / block / parry attempt, not even a late one.

They might think the enemy is intentionally ignoring defence (like reckless attacks) if that can be part of a coherent picture of what's going on.

But if something gives the character advantage, the character and player should both know about it. The trick is going to be coming up with a reason why that makes sense to them other than being toyed with.

Answer 8

Attacks: as GM you can give disadvantage for any reason Defenses: If you want to leave their ac as is you can create a threshold below their AC where you change how you describe how you narrate their actions in response to the players actions but leave their AC unchanged. Remember to ask for damage that you are not going to record or the players will get cognitive dissidence.

Answer 9

Yes.

Consider the following three points from the rules:

1. If do not (willingly or not) benefit Dexterity, you decrease your AC accordingly.
2. If you intentionally do not pay attention to your attack, stay motionless not even trying to avoid attacks or close your eyes, then the attacker has advantage on the attack roll.
3. You could intentionally merely hold your shield instead of wielding it. As per rules you need to wield your shield in order to benefit from its AC bonus

Just those three things could severely impair AC.

Of course, there is a 'common sense' limitation of how far you can lower AC. For example: Someone wearing full plate armor cannot lower their AC below what the basic armor provides (including magical bonuses). Full plate armor is hard to bypass even if the wearer is not moving and not even trying to avoid the blows at all.