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My 5e group has reached level 5 and all have acquired +1 weapons. This renders the monster ability of "resistant to bludgeoning, piercing and slashing damage from non-magical weapons" a moot point. It's possible they'll wind up in circumstances where they need to use improvised weapons, but for the most part, this monster ability isn't going to affect play.

This is unlike resistance to Fire or Lightning, in that those resistances don't go away when the players acquire gear.

The Effective Hit Points Based on Resistances and Immunities table (DMG 277) provides a multiplier based on monster CR, but doesn't address party level, which is a pretty strong indicator of the likelihood of the party having magic weapons.

Should I continue to use these now-moot resistances when calculating effective monster HP for purposes of determining CR?

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Do you reduce the CR of monsters with resistance to Fire or Lightning when facing a party with no Fire- or Lightning-based attacks, since the resistance doesn't affect that party?

I'm going to guess that, no, you don't, even though it doesn't affect play. Non-magical weapon resistance is no different. Some parties will be affected by the resistance. Other parties will not. But the monster remains the same, and should have the same CR, either way.

Madness lies down the path of adjusting CR to discount abilities which don't affect the PC party: "We need to have one spell of every element, so that all elemental resistances will contribute to CR. We also need one person with a non-magical weapon, so that non-magical weapon resistance will contribute. Etc."

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    \$\begingroup\$ Also....a creature that's supposed to have a CR of 10 but, due to your players having magical weapons and, thus, able to bypass it's defenses and making it seem more like a CR of 6...kind of works out in the player's favor. They are getting CR10 worth of experience for bringing down a foe that otherwise would have been more difficult had they not otherwise come upon those magical weapons they now have. Lowering that creature's CR just to compensate a weakness will take that accomplishment and, as a result, that EXP away from your players. Let them keep the spoils of their advantage. \$\endgroup\$ – Airatome Mar 9 '15 at 11:57
  • \$\begingroup\$ Accepting this one because of the explicit parallel to fire/lightning, which I referenced in the question. And you're right, I'm not adjusting for the presence/absence of those, so I shouldn't adjust for the presence of magical weapons. \$\endgroup\$ – kevin.matheny Mar 9 '15 at 12:20
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    \$\begingroup\$ Just because you have the key, doesn't mean the door isn't locked. You just have the means to open the door, but it's still a locked door. \$\endgroup\$ – Escoce Mar 9 '15 at 15:30
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    \$\begingroup\$ Plus having the required magic weapon may not be everything you need. What if you're disarmed of the weapon? What if you have NPCs in the party? What if there's a TWF with only one magical weapon? There are lots of ways this can affect the party. \$\endgroup\$ – Gates VP Mar 10 '15 at 0:10
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    \$\begingroup\$ @GatesVP If I were a monster only vulnerable to magical weapons, disarming people would be my favourite trick. \$\endgroup\$ – GMJoe Mar 10 '15 at 0:27
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The scenario you describe is a perfect example of the Tiers of Play discussion on page 15 of the player handbook. This edition of D&D is divided roughly into four tiers, the first tier comprising the first four levels, and the second tier comprising levels 5-10.

Upon reaching 5th level, characters gain access to 3rd-level spells, find valuable magic items, and pick up class abilities that completely change their effectiveness and style of play. Foes that were once quite challenging due to abilities such as resistance to non-magical weapons, are now not so threatening.

The distinction here is that the creatures are no less threatening to the community at large, but are far less threatening to your players simply because your characters are on a whole new tier of play.

But does that make the foe less worthy of granting XP?

Indeed it does; however, this has already been accounted for in the Character Advancement table (also on page 15). Advancing from 5th-level to 6th-level requires an additional 7,500 XP, which is more XP than your characters accumulated to progress all the way from level 1 to level 5. It takes a lot more of this now-inferior foe to contribute meaningfully to your characters' progress. As such, there is no need to manipulate its CR.

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  • \$\begingroup\$ Well said. Why couldn't I be as eloquent in my answer? :D \$\endgroup\$ – Airatome Mar 10 '15 at 11:49
  • \$\begingroup\$ Excellent point - I hadn't considered the character advancement table! \$\endgroup\$ – kevin.matheny Mar 10 '15 at 13:20
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I would say yes, the CR should stay the same. Why? Let's say you had all encounters for the entire campaign pre planned, pre written, and already established. You have creatures spread out through your campaign with said resistance to non magical Blunt, Piercing, and Slashing damage. Just because your players have found magical weapons and can now pass said resistance, doesn't take that away from the creature. it's an inherent ability, it exists, and thus it counts... be it moot or otherwise. What happens if they break their +1 weapons in some other encounter? Or they use some other means of launching an attack without using their magical weapons, then it still helps to know that piercing damage from that arrow trap they pushed the monster into deals 1/2 damage, not full damage, to the creature with said resistance.

The charts/tables are designed that way for a reason. They can't possibly take all party levels and items found into consideration...it's too much randomness. Characters in a campaign I'm playing in are level 5 nearly 6 and NO magical weapons have been found so far. So those resistances would still be effective against our group. Meanwhile in the Campaign I'm running; I've designed one magical item targeted at each party member for them to find at various stages in the game.

The other thing is, nothing is stopping you from doing a test run and seeing how it goes. If you think the encounter begins to swing largely in the players favor because they're bypassing the resistance at level 5? Feel free to change the CR rating and/or give it more HP and things of that sort to toughen up the encounter and make up for the sudden lack in defense it used to have.

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  • \$\begingroup\$ I get that the tables can't take all parties and games into account. But I can take my party and my game into account; as intended the tables are using the multiplier on hit points from the resistance to affect the difficulty of the monster. The thing I'm getting at is that for my current players, that multiplier isn't there, so the resulting effect on CR isn't justified. The monster is easier to defeat than the CR would indicate. \$\endgroup\$ – kevin.matheny Mar 9 '15 at 0:15
  • \$\begingroup\$ @kevin.matheny As I said, the multiplier IS there, it's just seemingly redundant...and as redundant as it may be, it still exists one way or another. The rules are very precise, which makes all resulting effects on Challenge Ratings justified; in the books/rules department at least. As a DM, however, you have power to alter, change, or ignore entirely said rules justifications. If the monster is easier to defeat than the CR indicates; then refer to my last sentence. Nothing stops you from altering it. Give it a lower CR/EXP, or give it extra features/HP/damage output to compensate. \$\endgroup\$ – Airatome Mar 9 '15 at 11:49
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I'm in a situation that is similar, and my answer has been to simply add the multiplier to the health of the enemies and remove the resistance to non-magical weapons.

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  • \$\begingroup\$ Welcome to RPG.SE! Take the tour, and check out the help center for more guidance. \$\endgroup\$ – V2Blast Feb 8 at 3:40

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