The DMG p. 105 states

Brown mold is immune to fire, and any source of fire brought within 5 feet of a patch causes it to instantly expand outward in the direction of the fire, covering a 10-foot-square area (with the source of the fire at the center of that area). A patch of brown mold exposed to an effect that deals cold damage is instantly destroyed.

For a party without spells dealing cold damage, what mundane/non-magical alternatives are there that could destroy or otherwise nullify the risks of the mold? Could a character with sufficient scientific knowledge create dry ice, for instance? What about acid?


2 Answers 2


Brown Mold isn't immune to everything

It's only immune to Fire damage, and is particularly vulnerable to Cold damage, and that's it. Which means any kind of damage other than the two listed above would still damage the mold- and eventually destroy it.

  • Acid? Sure, but don't expect it to clear a 10x10 patch of it, so you'd need a lot of acid.
  • Bludgeoning? Slashing? Maybe. How exactly does the player want to achieve it? (Hint: A Ten-foot pole is required)
  • Piercing? Ugh... No.

As always, use your best judgement on how effective a certain type of damage is. Be open to proposed solutions and reward player ingenuity, if it's fun for the table, you're doing it right.

Additional guidance on Object's Hit Points and AC can be found in DMG 246. I would personally rule that a patch of Brown Mold is a Large Resilient Object with similar AC to soft objects. Based on the tables, that puts it at AC 11, HP 27.

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    \$\begingroup\$ You might want to clarify that this is a suggested way to handle the situation, but not necessarily RAW. It seems likely that the designers would have given us those stats directly in the description, had that been the intent, rather than for DMs to infer it from a set of vaguely directed assumptions. The mold doesn't take damage in any rules sense. Note that the word "damage" is not used in the description. Fire and cold have effects on it. The mold is meant to be a Dungeon Hazard, not a creature one bashes or slices. \$\endgroup\$ Commented Oct 12, 2017 at 13:37

The Blight spell (4th level) works wonders for a party facing mold infestations of any kind-- while the larger oozes get to be creatures and thus 'merely' take (half, probably, of) 8d8 necrotic damage, non-magical plants (which includes molds; D&D runs on the medieval taxonomical system) just straight up die, no save.

The spell Speak With Plants (3rd level) is even better. Unlike most normal, non-magical, non-creature plants, brown mold does possess a method of rapid locomotion-- growth in the presence of fire. Using speak with plants you can ask the mold not to hurt you and your companions, and to come with you to fight your enemies. Using a standard torch, you can then lead it along a wall of the dungeon to fight off whatever else you run into down the line. Just make sure you don't run out of duration before you leave the dungeon, or, if you do, make sure you have a secure place to camp which the now-massive-and-no-longer-allied mold can't intrude into.

If you lack spells entirely, you'll need to improvise. As a non-creature, brown mold lacks any explicit requirements for things like air, sleep, food or hit points, but it may still need some of these things to survive. The only method that definitely doesn't work is fire damage, and the only methods that definitely do work are cold damage and effects that explicitly say they can kill/destroy noncreature plants.

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    \$\begingroup\$ To clarify, casting Speak With Plants could render a patch of Brown Mold inert or even friendly for characters in its effective range of 5 feet? Could characters step on top of the mold patch with a lit torch, for instance? \$\endgroup\$
    – MonkeyKB
    Commented Oct 12, 2017 at 8:09
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    \$\begingroup\$ @MonkeyKB Yes, but that's a bad idea because then the mold would grow all over you and it'll stop being friendly at some point. Walk across the mold, then light the torch. Make sure you're never in-between the fire and the mold. You also don't have to intentionally grow it if you suspect it'll become too dangerous to manage. \$\endgroup\$ Commented Oct 12, 2017 at 8:11
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    \$\begingroup\$ Do you have a citation for molds qualifying (for D&D purposes) as plants, ideally from a 5E source? It seems clear to me that Blight should have the effect you describe, but I'm not sure how much the text supports that interpretation. \$\endgroup\$ Commented Oct 12, 2017 at 19:31
  • \$\begingroup\$ @RyanVeeder The idea is that everything falls into a kingdom of the Heirarchy of Creation/Great Chain of Being, as an extention of the medeival setting: God, Angel/Spirit, Man, Animal, Vegetable, Mineral, Nothing. This is strongest in early editions of the game, but as spells are forward-ported it has stuck around, and as everything in 'Plant' having one type is mechanically convenient, that's stuck around too. Citations would be very lengthy to build a convincing case, because I'd be collating spells like polymorph and creatures to show that animal, vegetable, and mineral are complete. \$\endgroup\$ Commented Oct 12, 2017 at 20:52
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    \$\begingroup\$ Why would being friends with the mold mean it doesn't damage you? \$\endgroup\$
    – Miniman
    Commented Oct 12, 2017 at 21:15

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