Don’t Make Me Remember that You Have Magic Armor

Another house rule we’ve recently adopted in the White Sandbox is that instead of affecting your armor class and thus your chance to be hit, each +1 worth of magical protection gives you a 1 in 10 saving throw against the effects of the hit.

Let’s say that Caswyn of Apollo is wearing one of the Gray Company’s namesake +1 cloaks of protection when he is struck by a medusa’s dagger. Caswyn’s player Eric calls out two numbers on a d20 and rolls it. If either of Eric’s lucky numbers come up, Caswyn’s cloak of protection has stopped the blow; he takes no damage and doesn’t have to save vs. the poison on the dagger. If Caswyn also has a +1 shield and +1 platemail in addition to his cloak, Eric gets to roll three d20s; of his lucky numbers come up on any of them, his gear saves him from harm.

The idea behind this house rule isn’t to change the statistical benefit of magical protection. Some rough analysis suggests that a 1-in-10 armor save helps you slightly more than a +1 to AC when you’re facing a high hit dice creature, and slightly less against a weaker enemy whose base chance to hit you is small. I see this as a nice side benefit, but the point is to change the way that magic protection feels. (For example, even if both are statistically equivalent, I think there is a very different feel in older editions when the target of a charm spell makes a saving throw and avoids its effects, versus in 4E when you make an attack roll for the spell and miss.)

A guiding principle for this house rule and the one about not rolling your hit points until you’re hurt is to take aspects of the game that normally get resolved off-screen beforehand and instead make them happen at the table as the spotlighted consequence of a dramatic event.

As the DM I roll to hit the PCs many times in an average session. When one of those blows would have landed if not for the protection of Fred the talking magic amulet, it’s obvious only to me. Even if I use this fact to narrate the monster’s miss, it doesn’t seem as real to the player as if I say “The minotaur’s axe slices you for six points of damage” and they get to respond “Not so fast, let’s see if Fred can save the day!” Owning a magic item, and being able to survive a lethal blow, should be remarkable. Highlighting these with a separate resolution step in play makes sure they get remarked upon.

It’s also extra work for me to have to figure out why a roll misses someone due to magic items. The armor save house rule unloads some work onto the players. One of the things I like about “three little books” OD&D is that AC can be directly translated into armor type. When we don’t use modifiers to AC from Dexterity or magic items, I simply track whether PCs are wearing leather, chain, or plate and then figure out AC from there. If AC is instead a complex composite of factors I have to remember both what a character’s AC is and also what armor they’re wearing, with all the other things that implies.

Another great thing about OD&D is that there’s a narrow range of AC. Even in magical plate and shield, a fighting man needs to worry about being hit by a lowly man-at-arms 20% of the time. I like this because even if a PC’s magical protection will stop a blow most of the time, I want to make the players sweat in the interval between when I announce the hit and when their magic save comes through for them! Also, when I have dozens of men-at-arms in the combat it’s much easier if I can just roll a handful of dice and count all the 17s or above, knowing that such rolls always have a chance of hitting any target.

Two final notes to put this house rule in the context of the original rules and in actual play. The text about magic armor and shields in Monsters and Treasure says that “Armor proper subtracts its bonus from the hit dice of the opponents of its wearer. If the shield’s bonus is greater than that of the armor there is a one-third chance that the blow will be caught by the shield, thus giving the additional subtraction.” Rather than try to reconcile the Arnesonian, Chainmail-based proto-D&D implications of that with the alternate-combat-system under which we normally roll, I’ll simply appropriate the idea of the probabilistic protection of a magic shield as support for the spirit of this house rule.

The need for these house rules came from a newfound prevalence of protective items  in the White Sandbox campaign. This emerged because, until last session’s return to the Caverns of Thracia, we’d been looting nearby destinations in Jaquaysland, like the Fabled Garlin of Merlin (The Dungeoneer #2, editor) and Borshak’s Lair (The Dungeoneer #3, author), as well as one unique to the campaign, the workshop of the lich Patariki Van in the Nameless City. The consequent increase in bling was purposeful; I love the Caverns, but their distribution of loot doesn’t leave adventurers well prepared to face the stiff opposition in its deeper levels. (At EN World, Bullgrit has raised similar complaints about B1: In Search of the Unknown. Evidence of an anti-“Monty Haul” backlash taking place between 1976’s rich hauls and the spartan offerings of TSR and Judges’ Guild in 1978-9?)

EDIT: Maldoor’s comment below reminds me of another rationale behind these rules: players like to search for anything that’ll save their bacon when a PC’s life is on the line. In more rules-heavy games, the party goes modifier hunting: “Did you remember your temporary hit points? Did the monster hit even with its -2 to hit from bane?” Having a rule that kicks in at this tense moment will hopefully replace the urge to rules-lawyer and find ways to retcon it didn’t happen. Also, a game in which a character is never in danger because of their unhittable AC is boring; one in which that same character is quickly brought to the edge of death because they don’t remember to make their armor saves until it really counts is exciting!

11 Responses to “Don’t Make Me Remember that You Have Magic Armor”

  1. March 1, 2010 at 4:24 pm

    I wasn’t so keen on the last post about rolling HP when you get hit–I like the idea, but it seems like it would possibly be a bit too much trouble (I will probably try it anyway, because I love testing all of your guys’ house rules). This, however, is great. I am definitely going to be incorporating this into my S&W campaign once my party gets high enough to get some +protection items. Thanks for the great house rules!

  2. 2 maldoor
    March 1, 2010 at 5:35 pm

    As a player in Tavis’ game, I admit I was curious about how this rule would work. My worry was the increase in complexity would eclipse the excitement payoff. In our session yesterday, I thought the excitement at the rolls was worth it, especially as we got used to the idea and wove it into our combat routine.

    In addition to a set of exciting (possibly lethal!) rolls for players, there is a second possible bonus. This system encourages players to be more present in the moment of the game – if you are phoning it in, you may very well forget your bonus items (and I do not see it the role of the DM to keep track and remind each player of such things – the DM has a lot to keep track of as it is). Not to be punitive, but anything that keeps the attention of everyone at the table together is a positive, in my opinion.

    Another example of this is our house rule for bandaging: it only works if it is the first thing you declare upon finishing combat. At first, a lot of people forgot, and Tavis was diligent about listening to what players stated they were doing. A lot of us lost what are essentially free hp’s. Now when combat is over, half the table is poised, waiting to remind each other to bandage first… It is cool when everyone is so focused.

  3. March 1, 2010 at 6:00 pm

    Good point, Maldoor – in fact I think I’ll edit that into the main post.

    Might you be tempted into doing an investigation of whether two or three 1-in-10 saves is equivalent to a +2 AC? (I’ll email you the Excel sheet I made up to do my brute force analysis).

    Also, what do you think of implementing an AC bonus from high Dexterity using this system? I’ve avoided doing so because of not wanting to pollute the possibility of doing weapon vs. AC and the other reasons that I cite, but as it stands I think being mighty is substantially better than being skillful and it’d feel very pulp to give skillful characters a spotlight chance to dodge a blow.

  4. March 1, 2010 at 6:20 pm

    That is a fun idea, glad to hear that it is working out well in play.

  5. March 1, 2010 at 11:02 pm

    It seems to me that a +1 to AC would be equivalent to a 5% chance to resist any attack, as attacks are made on a d20, rather than a ‘weighted’ roll like 2d10. Why would the +5% chance translate to a 10% chance to resist damage? I mean, it’s possible that my math is wrong (say, the +to-hit affects it more).

  6. March 2, 2010 at 12:01 am

    I thought so too, but in this thread Maldoor made a table saying it wasn’t so. I wasn’t sure I followed the reasoning, so I did a brute force analysis in which 100,000 attacks were made against fighting men of various ACs, conjured from Limbo for this purpose – this, rather than any actual understanding, is the basis for my saying that a 10% save is roughly balanced against a 5% reduction in hits.

    If I had to put it into words, I think it’s that +1 AC protects you against 5% of all to-hit rolls, but a 1 in 20 save protects you against only 5% of that subset of rolls that were actually able to hit you. But if you want to play with the Excel sheet I made to test such things out, email me at Gmail; my address is first name.last name.

  7. March 2, 2010 at 2:29 am

    Awesome rule. I loves it as I’m really wanting to keep AC Armor Class and not a bunch of other junk.

  8. March 2, 2010 at 2:44 am

    “think it’s that +1 AC protects you against 5% of all to-hit rolls, but a 1 in 20 save protects you against only 5% of that subset of rolls that were actually able to hit you”

    Oh! Yeah, that makes sense. Thanks for answering! I guess otherwise it would only protect you from, say, 5% or 25% of attacks. Gotcha. Still love the rule.


  9. 9 maldoor
    March 2, 2010 at 3:01 am

    Brenton, good question. Frankly, I am suspicious of my math (since I was goofing off in high school, playing D&D when I was suposed to be learning it…) The table in the below post is how I convinced myself. I added the expected damage into the chart so there would be a single number to compare under each scenario, to rank them, but now that I look at it, probability would be simpler.


    I think Tavis got the explanation right, above, in terms of probability: applied to AC it blocks 5% of hits. Applied as an effective 5% save vs. damage once you have been hit adds up to different numbers, but is usually less than 5%.

    In the example in the chart, the adventurer has a 30% of being hit with AC:4. With AC:3 they have a 25% of being hit. If you apply the 5% as a save, then the chance of being hit with AC:4 is 30% minus (.05*30%=1.5%), or 28.5%.

    But this changes with the relative AC. So if our adventurer is unarmored, AC:9 he has a 55% of being hit. Give him +1 protection, and AC:8, and he has a 50% of being hit. Apply the bonus as a 5% save sv. damage, and the effective chance of being hit is 52.25%. Better, but still not as good as applying the bonus directly to AC.

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Past Adventures of the Mule

March 2010

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