OSR: Arms and Armour: The Power of Plate

OSR-type-games traditionally use one number to represent how hard a character is to hit. For the purposes of this article, we're going to call that number Armour Class (AC).Dexterity (the stat) might increase* that AC. Wearing armour also increases AC*. The higher** the number, the less like a character is to take damage.

*Or decreases, if you're using descending armour class, but you get the idea.
**Or lower, see above.

And that's usually fine. It's just a game after all. It's not a game about armour or even (arguably) a game about fighting.

But it's also not very realistic. Armour doesn't work like that.
Desperta Ferro no 4

How Does Armour Work

I'm going to lean on this article by fairly heavily. It (and the entire blog) explains complex topics in a clear, pop-culture-accessible way. You can also look up hundreds of videos of reenactors and enthusiasts doing surprising things in armour.

Armour is good. Humans are squishy. Everyone who could afford to wear armour did. "Afford", in this case, means both financially and energetically. Armour is heavy; if you can't do your job while wearing it, you'll die anyway.

Why Realism?

Because the real world, particularly the past, is interesting, weird, and unintuitive. If you can make realistic things work in your games, they can add a layer of complexity and value.

If you can't, they can add a layer of tedious and pointless bookkeeping. There are a lot of systems out there that claim to "fix D&D" by emulating "realistic medieval combat". Nine times out of ten, they're enthusiastic and detailed but utterly tedious. Stances and guards and fifty different kinds of polearms. Rules for every helmet. There's a market for that kind of complexity, but I like simple rules to explain complex concepts.


Cost and Abundance: tend to only matter in the first few sessions. Once the PCs have money, they'll try to buy the best gear locally available.

Inventory Slots: a better trade. The more Inventory Slots you fill with Armour, the fewer you have for weapons, tools, and supplies. (Inventory Slots are equal to a PC's Strength score, or 10, or 12, or some other arbitrary but low number.)

Stat Penalties: a strange trade. The better your armour, the fewer roles you can perform. You are less likely to set up an ambush and more likely to be caught while running away.


It's the 14th century... ish, Europe... ish. Full plate armour exists, but is not particularly common. Firearms and cannons are primitive. Everything exists in a murky transition between feudal power and monarchical states. Mercenaries are becoming more common. Wizards are present, but not common and not apocalyptically powerful.

Damage Types

For clarity.

Slashing. The most common type. Animals with claws, swords wielded by untrained users, etc. If you can do it with a bread knife, it's Slashing damage. Makes a horrible mess of unarmoured flesh but is defeated by most armour.

Piercing. Pressure applied at a point. Daggers, arrows, crossbow bolts. Arrows are a borderline case in some ways, but I didn't want to give them a separate damage type. Piercing damage punches directly through armour or, more likely, hits a weak point like a joint or a gap.

Bludgeoning. Pressure applied broadly. Hammers, chair legs, trampling. Big bruises, concussions.

Crushing. Unstoppable pressure. A hippo's bite, falling off a cliff, a hammer trap, etc. Turns plate armour into a squashed tin can. Typically, not reduced by armour or spells. Firearms and cannons might deal Crushing damage.

Elemental. Acid, Ice, Fire, Ice, Lightning, Stone (maybe? Might be covered by other damage types), Void (Sonic), and Water. Stuff you can't avoid, even in armour. Hot sand or oil deals fire damage.

Magic. The darkest magic. Or just regular magic. Bypasses mere metal, leather, and flesh. Sometimes deals damage directly to a creature's soul.
Branca branca branca!


Leather Armour

"Leather Armour" is fictional; armour made of leather existed. This tier covers quilted fabric, fish leather, wood, hide, etc. It's cheap. It's abundant. Leather Armour occupies 2 Inventory Slots and reduces incoming Slashing damage by 3. It does not penalize Stealth or Movement.

Chain Armour
Chain armour is expensive. It occupies 4 Inventory Slots and reduces incoming Slashing damage by 6.

Plate Armour
Very expensive. It occupies 6 Inventory Slots and reduces incoming Slashing and Bludgeoning damage by 6, and Piercing damage by 4.

Common. A Shield occupies 1 Inventory Slot and must be wielded in 1 hand. It reduces incoming Slashing, Bludgeoning, and Piercing damage by 2. A shield can also be sundered, destroying it but reducing incoming damage from one source by 1d12.

Magic Armour
Very rare, possibly temporary, possibly cursed. Reduces incoming Magic damage by some amount. Enchanted shields, amulets, charms or caps are also viable. Magic Armour can also decrease or completely negate Elemental damage.

Bits of Armour
You can subdivide armour into pieces, granting fractional bonuses or using hit locations. That seems like a lot of effort to me. Yes, a steel helmet and breastplate with limited other armour is realistic, but it rarely seems to come up in play. Either a PC can afford a full suit and wants the full benefits, or they can't and don't.

Axel Sauerwald


This list is not exhaustive, but should let a GM assign both damage and size to most weapons.

Improvised weapons typically occupy either 1/3rd or 1 Inventory Slots. They deal 1d4 damage and can be thrown 10'. A shield can be used as an improvised weapon.

  • Broken Bottles: Slashing
  • Rocks, Chairs: Bludgeoning
Light Weapons occupy 1/3rd of an Inventory Slot. They can be thrown 30'.
  • Daggers: Piercing

Medium weapons occupy 1 Inventory Slot. If wielded in 1 hand, they deal 1d8 damage. If wielded in 2 hands, they deal 1d10 damage.
  • Swords: Slashing or Piercing
  • Axes: Slashing
  • Hammers: Bludgeoning
Heavy weapons occupy 2 Inventory Slots. They deal 1d12 damage and must be wielded in 2 hands.
Big Swords Slashing or Piercing damage.
  • Big Swords: Slashing or Piercing
  • Big Axes: Slashing
  • Big Hammers: Bludgeoning
Reach weapons occupy 2 Inventory slots. They deal 1d8 damage, but let the wielder fight from the second rank of a formation, where they can't be hit by anything but Reach or Ranged weapons. They must be wielded in 2 hands.
  • Spears: Piercing
  • Complicated Polearms: Pick a damage type pair. Slashing and Piercing. Slashing and Bludgeoning. Piercing and Bludgeoning. Though I'd suggest making Bludgeoning damage harder to find, or reducing its damage to a d6.
Ranged weapons occupy 1 Inventory Slot and have a base 30' range. They must be wielded in 2 hands.
  • Bows: 1d6 Piercing
  • Crossbows: 1d12 Piercing. Takes 1 round to reload.
All melee weapons add the wielder's Strength bonus (usually 0, sometimes +1 or -1, occasionally +2 or -2) to their damage.

Magic weapons either add Magic damage to an attack, or turn all the attack's damage into Magic damage (or Elemental damage).

  • A +2 Dagger might deal 1d6 Piercing damage and 2 Magic damage, or it might deal 1d6+2 Magic damage. Depends on your system and preference.
  • A +2 Dagger of Fire might deal 1d6+2 Fire damage, 1d6 Fire damage and 2 Magic damage, or 1d6 Piercing damage and 2 Fire damage. Again, there are a few ways to divide damage.

Additional Rules Clarification

Attack rolls vary with system, class, level, etc, but should be somewhere between 50% and 90%, in ideal conditions. Critical Hits, (a 1-in-20 chance) deal double damage.

Being prone reduces damage reduction by half. Depending on the system, prone targets may also be easier to hit with melee attacks. "Prone" covers conditions where a target is easier to hit. The more you can do to imperil or impede your target, the better your chance to hit.

Osprey #155

Fearful Symmetry

You can start to see how it all fits together.

Wearing Plate armour and carrying a Shield (the best available mundane defense) reduces most incoming damage by at least 6... but at a cost. A PC's damage output is reduced (because they can't wield a 2-handed weapon). 7 of their very limited Inventory Slots are full of stuff that's only useful in combat, 8 if you include a weapon.

Plate without a Shield still fills up 6 slots. Piercing weapons can sneak through a few extra points of damage, but in return, a PC can wield a mighty two-handed weapon and deal some significant pain.

Chain is a decent compromise. Damage reduction against the most common form of damage, especially in a dungeon, but relative vulnerability to both Bludgeoning and Piercing damage. A shield helps cover those gaps.

Leather only occupies 2 Inventory Slots, so it's viable for low-capacity PCs, or PCs who need to carry a lot of other items. It doesn't penalize Steath or Movement, so sneaky-types can wear it without fear.

No armour is also viable. If you don't get hit, you don't need to worry about damage reduction, and there are a lot of ways to not get hit. And you've got all those sweet Inventory Slots to fill with items that can save your life, or get you rich, in non-combat situations.

Inventory switching becomes a critical issue. In the GLOG, the first 3 Inventory Slots are quick-draw, meaning a PC can access them immediately. They could be weapons, vital tools, spellbooks, a lantern, etc. Anything else requires 1 full round to access.

If a PC wants to focus all their resources on combat, they may want to pick Plate armour (in their general inventory), a Shield (in 1 quick-draw slot), a Sword (in 1 quick-draw slot), and... well, something else. With 9 Inventory Slots full of stuff, and with weapon and shield at the ready, they're in trouble if they get into a non-combat situation. Holding a lantern or torch will be difficult; they'll need to drop it to draw their sword and raise their shield.
Cavalry charges hurt.

Rock Paper Scissors... Lizard Spock

The discussion so far has focused on equivalent arms and armour: fights where both sides have the same tools and tactics. But typical dungeon inhabitants change the considerations.

Giant Spiders, Centipedes, etc.
Armour as leather (-2 Slashing damage) or unarmoured. You could also add bonus damage from bludgeoning sources. Chitin is fragile. They typically deal Piercing damage (bites), plus secondary effects (poison, paralysis, etc.)

Goblins, Kobolds, etc.
Unarmoured, or Leather (-2 Slashing damage). Some organized goblins might have shields (-2 Slashing, Bludgeoning, and Piercing damage). They typically deal Piercing damage (daggers,  spears, arrows).

Orcs, Hobgoblins, etc.

Leather (-2 Slashing damage) or Chain (-6 Slashing damage). Sometimes Shields (-2 Slashing, Bludgeoning, and Piercing damage). Rarely, Plate (-6 Slashing and Bludgeoning damage, -4 Piercing damage), but typically with two-handed weapons instead of with a shield.

Mimics, Giant Rats, Zombies, etc.

No armour. Typically deal Slashing or Bludgeoning damage.

Skeletons, Golems, etc.
Immune to Slashing and Piercing damage. Typically deal Slashing or Piercing damage.

Typically immune to Piercing damage. Frequently have other immunities. Typically deal bludgeoning or acid damage.

Ghosts, Liches, Other Horrible Things, etc.
Immune to everything except Magic damage. May take some types of Elemental damage. Typically deal Magic damage.

The conclusion seems clear. Bring many damage types, switch between them, and try to either deal Elemental or Magic damage. But rarity, risk, cost, and lack of inventory space will by necessity limit these options. There's no optimal solution, but there are a lot of interesting solutions. And that's very appealing.
KILART (choe, heonhwa)

Dungeon Tactics

Dungeons are weird environments. Medieval warfare is not designed for 10' hallways, pit traps, and goblins who can see in the dark.

Arms and armour adapt to the pressures faced by their users. Time lag exists, as it always has (and in some fields, always will), but it's worth examining what pressures medieval armour faces underground.
When history moved slowly, as it did before 1900, rulers were slow in learning realities in the exercise of government, and some, like the Bourbons, never learned at all. It took a very long time before rulers came to realize that armed service would have to be paid for or that they needed to concern themselves with the wants of the lower orders from whom their armies were drawn. We have been living since under Henry Adams’ law of the acceleration of changing times, which obscures for us the time lag that existed for our ancestors between the fact of change and the social and political understanding of what had happened.
-The First Salute: A View of the American Revolution

How the "fact of change" and the "understanding of change" will depend on your setting. Is crypt-robbing an established profession, with guilds and a long history? Arms and armour will reflect this. Is it new or sporadic? Arms and armour will be adapted, sometimes imperfectly, from battlefield use.


Rolling, dodging, leaping, and climbing are all feasible in full plate.

Mines are warm, but so is the desert, and people wore full plate in the desert. Not worried.

Evidence exists that it's possible, with effort, to tread water and swim along the surface for a few minutes in plate armour. I've yet to see anyone ascend from the depths in plate armour. Drowning is still a very real possibility if someone falls into water or is carrying other heavy items. Just because it's possible doesn't mean it's sensible.

Visibility and Awareness

Armour is noisy. A good helmet, by necessity, restricts vision and hearing. Both are flaws in a dungeon. Corridors echo. Pit traps and ambushes are obscured. I'd expect to see a lot of helmets with folding fronts or visors, so an armoured warrior could switch from scanning mode to combat mode immediately. Forgoing a helmet entirely is still silly, unless you're storing your brain elsewhere.

Cavalry combat is useless underground. Horses are great on an open field. You can't joust, you can't practice a full-speed charge, and you can't rely on your fellow explorers. They're just in it for the gold, after all.

A wall of spears and pikes is still formidable... if you can get it to hold. A formation 30 across and 3 deep is sturdy. In a confined space, with no room to maneuver, wheel, or retreat in good order, that same formation in miniature is very vulnerable to disruption. One fireball, one panicking hireling, one lucky goblin, and the whole formation goes to hell. It doesn't have the width to fill gaps.

So I suspect most "realistic" dungeon fights would be two small groups encountering each other, sizing each other up, possibly charging to within 10' or so, and then, after some posturing, retreating.

Dungeon combat requires much more tactical finesse than most armies in the 14th century could manage. Groups need to coordinate and execute complex plans. They need to adapt to unprecedented situations.
Hirelings and Followers
Morale is crucial. People typically won't fight to the death. If they do, it's usually not for high ideals or promises of gold. It's because they want to protect themselves or the person next to them, or because they fear being shamed or outcast for their behavior. That's it.

A peasant hired to hold a torch will be quaking in their boots at every noise underground. At the first sign of combat, they're gone. Running is almost always a better answer than fighting.

A combat hireling will fight based on their leader's charisma; the personal bond between leader and follower, the expectation of a culture, the pressure of tradition. Better pay will help get your hirelings to combat but won't nessesarily hold them in line. A share, or a half-share, instead of wages binds the hireling to a group; they feel like they're part of a unit, not a disposable accessory. Morale tests and reaction rolls are critical.
Spare Shields and Weapons
It's definitely worth giving a shield or two to a hireling, but in a combat situation, retrieving a spare shield might not be viable. Access to a variety of weapons is also good.

Marching Order
For groups of 4 or more, marching order becomes critical. Who's in front? Who's watching for ambushes from behind? Where's the squishy wizard?

The most common plan seems to be to put your best fighters in front, your squishy support people in the middle, and backup fighters behind.

Ranged attacks in cramped quarters are tricky. Firing into melee is very dangerous (thought that might not stop a suitably motivated PC). In larger rooms, the ability to deal damage without putting yourself at risk is valuable.

Pedro Krüger Garcia


This system can make some dice rolls meaningless.

Traditional One-Number Armour Class

  • It's your turn to act. You roll a dice. It's not a hit. Nothing happens. Boo.
  • It's your turn to act. You roll a dice. It's a hit. You roll and deal damage. Yay!

New Damage-Reducing Armour
  • It's your turn to act. You roll a dice. It's not a hit. Nothing happens. Boo.
  • It's your turn to act. You roll a dice. It's a hit. You roll and deal damage. Yay!
  • It's your turn to act. You roll a dice. You hit! Yay! You deal damage. Nothing happens. Boo.
Instead of a binary outcome (failure+no damage;success+damage), you've got 3 outcomes, 2 of which end in disappointment (failure+no damage;success+damage;success+no damage).

You could switch to an auto-hit system like Electric Bastionland. All attacks hit; armour reduces damage. Situational bonuses and penalties increase or decrease damage dice size or add extra dice.

But E.B.'s system doesn't really support leveling progression. You're as good as you're going to get when you start. Leveling (such as it is) improves your HP, but doesn't really change your effectiveness.

It require a bit more math. Modifying a standard character sheet to list all available damage reductions should save time. I'm not sure the tradeoff is worth it.

I'm still fiddling with these numbers, but that's the beauty of the concept. Once you've chosen your variables, you can change the values to suit individual tastes. If you think Leather Armour should provide more protection against Piercing weapons, add it.


Arise My Minions
It makes mass combat math easier. The GM could roll all the attacks individually, but rounding methods save time.

40 goblins armed with daggers (1d6, piercing) attack a knight in plate armour and with a shield (reducing incoming piercing damage by 6). Goblins have a base 50% chance to hit, so 20 attacks hit. Of those, 1 is expected to be a critical hit, so the GM rolls 1d6x2. The Knight takes that much damage, -6 of course.

If the Knight is knocked prone, the goblins have a 70% chance to hit. 28 attacks hit. 1 is expected to be a critical hit, but all 27 other attacks deal 1d6-3 damage. Ouch.

Don't get knocked prone. Goblins will stick daggers in your eyes.

Rewards Versatility
Having a mix of damage types will almost always be rewarding. There's not one universal answer. Piercing damage is good. but some common dungeon creatures (skeletons and oozes) negate it completely. Ranged weapons are good, but you might not be able to use the. Etc. Again, it encourages interesting choices and compromises.

Alters Expectations

It's easy to tell a story about the past that fits our current notions. Just a big pile of tropes, reinforced by other bits of media that are also made of tropes, until any relation to reality vanishes.

Armour is good. Wear it if you can.


  1. Since you are fairly well read on medieval historiography, have you thought on reading Jans Frans Verbruggen? Or have you already checked his works before? Based on your previous posts I guess you might like him, he's one of the main authors of medieval military history.

    1. I've read "The Art of Warfare in Western Europe During the Middle Ages", though not recently. I should dig out a copy and refresh myself.

      Though of course warfare =/= D&D-type dungeoncrawling. Different considerations apply.

    2. I'd love to hear your thoughts on Verbruggen's The Art of Warfare and how applicable it is to RPGs in general. Dungeoncrawling might resemble tunnel siege warfare more, in a minor scale and with greater logistical risks for the party. I've not read any books specifically on medieval siege warfare yet, so if you could recommend something I'd greatly appreciate it.

      Since this post covers armour in role-playing games. Have you checked The Riddle of Steel? It isnt OSR, but portrays the advantages of armour very well. Song of Swords, which is a more detailed /tg/ successor, has many harnischfechten manuevers for dealing with armoured opponents in melee.

  2. I've chosen damage-reducing armor rules since The Fantasy Trip and Arcanum in the 80s. TFT tied armor to reductions in its DX stat, which was also its to-hit and spell-casting roll, but I like you way of filling inventory slots. I also like matrixing it with damage type, but it is crunchier and easy to forget to do.

  3. So is slashing damage just plain worse? Or does it do better critical hits or something and that's just not covered here?

    1. Yup, it's just plain worse against armoured opponents. It's easier to manufacture and lighter (though not a full inventory slot lighter, which is a bit inconvenient).

    2. I had the same impression, maybe you could balance it making slashing weapons roll twice the damage and keep the highest, in this way they are lethal against unarmored opponents but you still want to use other weapons against armours

    3. It might help to give slashing type weapons small bonuses, ie +1 to ac for swords or a bonus vs shields for axe types? Of course that would be be some additional complexity.

    4. Slashing is worse IRL... No animal hunts slashing random body parts. Just a few do mainly slashing damage and they always focus in vital parts to cause bleeding (like wolves who target the flanks and thighs and chase the prey until they tire).

    5. IRL, it seems like slashing weapons have a few advantages, but some might be harder to represent in the game without making it significantly crunchier.

      Can wound/disable arms and legs (particularly arms) more easily than thrusting weapons > depends on your wound system, you'd need some critical hit mechanic that can cause specific wounds.

      Can be used more easily at closer range > can be represented with daggers vs swords maybe, but differentiating different types of swords is probably too granular.

      Easier to hit with on horseback where precise thrusts are hard to do - this is doable in game, if rather niche, just give it a to-hit bonus.

      Slashing can attack at a greater variety of angles than thrusting, making it more unpredicatble to defend against > small bonus to hit maybe?

      Slashing leaves you more open to attack than thrusting since your arm and weapon have to go out to the side, but pairing a slashing weapon with a shield mitigates this – maybe slashing weapons give you a penalty to AC but not if you have a shield? Best if used in combo with the last thing so it's not just another strike against slashing weapons.

  4. This is something I think about quite a lot (I assure you that I am very fun at parties).
    Oddly enough I’ve come round to rather liking the standard AC system, roll-high-or-nothing-happens. I see high AC armour, like plate or chain, not as damage reduction but as damage -negation-, with AC representing coverage.

    A miss represents the attack hitting the armoured part of the enemy and more or less not accomplishing anything, while a hit represents striking through a gap in the armour. The higher the AC, the less gaps. So with something like a chain hauberk you have to aim for unprotected legs and arms, while with a plate harness you’re limited to going for eyes and joints.

    Of course this ignores the fact that, even if striking through layers of chain or other armour, a good sword hit can break an arm or similar, and entirely fails to take maces and other bludgeoning weapons into account, but it works well enough for my fevered mind.

    Really the ideal solution for me would be damage reduction for blunt weapons and large scale foes like giants and AC for human-scale other weapons, but that might be a bit too complicated for my poor players. Took em a couple of sessions to get that “no grog” was gorgon backwards. Love you lot if you’re reading this.

  5. I was looking at a guide on how to improve 5e combat. Basically, just give loads of monsters immunity/vulnerability to certain types of damage. Skeletons would be weak to bludgeoning, immune to piercing, knights would be immune to slashing, weak to any attacks while prone. That sort of thing. Basically forcing the same effect as the variable damage reduction, without the glut of numbers. Everything has a cost after all!

  6. If you use Strength scores from 3 to 18 (3d6), you can say that each inventory slot can be +/- 1.4kg which is just a bit above the weight of one sword. 14kg (Str 10) is 20% of the weight of a 70kg person (the average human, men and women). 20% of the weight is also the limit most animals can carry the entire day without tiring.

    1. I suppose the 3-18 scale is not linear, and encumbrance is not a factor of weight alone. The size of the items also matters. The slot system is abstract. When you consider that 1 slot = 100 coins, and coins can have different sizes and the metal different densities... I would not translate slots into actual weight.

    2. Medieval silver coins had around 1.something grams. Continental Europe weight a bit more than England coins. Everyone caused inflation using the coins. Continental Europe mixed other metals with the silver the coin size kept the same but England do not added other metals so their coin was smaller as the time passed. That being said and for simplicity, 1 slot is 1000 coins.

  7. I have a similar system, only you roll straight for wounds which depend on damage type and location (which can be randomized if no location was chosen). Wounds from slashes are worse on the limbs and less severe on the body, for instance. I've yet to try it but I have high hopes for it.

    Also, I don't think you would be very comfortable in plate armour in a dungeon. Maybe a breastplate and a helmet, but definitely not a full harness.

  8. Well thought out except for shields. Shields are great and block so many more attacks than usually accounted for in RPG combat. But...shields also work best in man vs man combat not too sure how well they'd function vs small yet strong oppponennts and large heavy hitters.

  9. Prof. DM on AC (https://www.youtube.com/watch?v=WJUDZpBuVJM)

    Arrows vs plate (https://www.youtube.com/watch?v=DBxdTkddHaE)
    Bows vs crossbows (https://www.youtube.com/watch?v=1w8yHeF4KRk)

    The videos above show that crossbows don't inflict more damage than a bow. Crossbows were slower, but required less training. It looks like crossbows were also superior inside closed space. Bows are very cumbersome in closed space, such as corridors. It was also much more practical to shoot from walls with crossbows than with bows, but that didn't matter when shooting from the field up to targets on the wall.

    I make that crossbows inflict 1d6 damage, as bows. However, bows attack with disadvantage from 5' corridors or from >50% cover. This disadvantage doesn't apply to crossbows. Crossbows are only slower.

  10. so cool! i've cobbled together something very close. Only real difference was leather added AC, plate added absorption. Other things in between doing some of both. It's not perfect, but maybe passes the fridge test. This is cool, but you're right the extra bookkeeping may or may not be worth it. Could drop damage types to simplify dramatically. It's also worth noting that recon has significat added value. if you know goblins are around the corner, plate will make you a god. If you know a dragon is around the corner, you're wearing is can you will be boiled in.

  11. Thank you, thank you for this post. Particularly for the recommendation of the acoup blog, phenomenal. You consistently do a great job of posting useful and interesting information sources.

    Also, I think the system you have here is a great way of differentiating weapons. I have one question though. Normally AC is used to calculate % chance to hit. You could keep AC, but with damage reduction as well it seems like you'd have double protection. Do you suggest any alternative method for to hit rolls? Like a d20 + attack bonus vs a fixed number (possibly modified by target's dex/size)? Or opposed rolls or something? Just curious.

  12. I have an idea I thought I’d share here. What if armour sets a minimum amount of damage that a character can take?

    Someone in plate can be hurt by a weapon, but only if it’s a powerful strike, and they’ll shrug off any attacks that deal less than, say 4 damage.

    This means that a powerful dragon breath attack will still harm them because it does so much damage, and opens up the possibility to ignore armour if, for instance, you have an armoured opponent on the floor and you have a dagger, rather than arbitrarily affecting AC by a right-sounding number