Ironrot Lichen

Small plant, unaligned

Armor Class 19 (natural armor)
Hit Points 110 (16d6 + 54)
Speed 10 ft., Climb 10 ft.

6 (-2) 21 (+5) 18 (+4) 1 (-5) 11 (+0) 5 (-3)

Skills Perception +6
Damage Immunities cold, lightning
Condition Immunities blinded, charmed, deafened, frightened, paralyzed, prone, stunned
Senses tremorsense 60 ft., passive perception 16
Challenge 7 (2,900 XP)


  • Camouflage. An ironrot lichen looks like normal rust and corrosion on a metal surface when at rest. A creature must succeed at a DC 22 Intelligence (Nature) or Wisdom (Survival) check to notice it before it attacks for the first time.
  • Ironrot Plague. The ironrot plague is a troublesome but nonlethal plague that affects metallic items. When exposed to either the touch of the ironrot lichen, or its spore cloud attack, any affected metal items are subject to its effects. Creatures that are holding or wearing metal items can make a DC 15 Dexterity saving throw to mitigate the effect. On a success, the metal items take 1d4 necrotic damage that bypass any resistances to damage. On a failure, the item becomes broken and unusable. Creatures made of metal (e.g., an iron golem) makes the same saving throw and takes 22 (4d10) necrotic damage on a failure, or half as much on a success. An item that fails the initial saving throw must make another saving throw after 1 minute. A broken item becomes destroyed on a second failure or remains broken and ends the effect on a success. Creatures that fail the first saving throw must make another saving throw every minute, taking damage on a failure, and ending the effect with no damage on a success. A creature or object destroyed as a result of this plague sprouts a new patch of ironrot lichen in 1 hour. Only metal creatures and held objects receive a saving throw against this disease; other metal objects automatically fail. Magic items are explicitly immune to this effect.


  • Multiattack. The ironrot lichen makes two tendril attacks.
  • Tendril. Melee Weapon Attack: +6 to hit, reach 10 ft., one target. Hit: 21 (6d6) acid damage. If the target is made of metal, wearing metal armor, or wielding a metal weapon, they and/or those objects are exposed to the ironrot plague (see above).
  • Spore cloud (Recharge 5-6). The ironrot lichen releases a 10-foot-radius cloud of spores. Creatures within the cloud must succeed on a DC 15 Dexterity saving throw or be affected ironrot plague (see above). Metal objects that are not held are automatically subjected to the ironrot plague as if they had failed their saving throw.


Ironrot lichens faced extermination in most inhabited areas after infestations of the plant wiped out armor, tools, and weapons, while spreading from settlement to settlement on tainted metal. The hardy plants went into a long dormancy in hidden areas and have thus far avoided complete destruction. Ironrot lichens can enter a long-term stasis, and they reawaken after many locations have forgotten about the massive damage they cause. They also thrive in extreme environments where they could reproduce through red-blooded creatures populating those environments. Patches of dormant ironrot lichen have also spread to airless locations in space, becoming a menace to miners who rely on metal tools and habitats on the asteroids they work. A patch of lichen takes up a roughly 3-foot-diameter space and is virtually weightless.

Contagious Corrosion. Rumored to be a creation of the Hegemony, ironrot lichens sprouted simultaneously on many worlds where they unleashed considerable devastation. The first ironrot lichens only corroded metal and spread slowly enough to allow infested metal to easily come into contact with other metal objects. Whether through deliberate or unintentional mutation, ironrot lichens metamorphosed such that they inflict caustic wounds to flesh, and their destruction of iron also extended to iron contained in a living creature’s blood. The lichens are immune to temperature extremes and even magical sources of cold, but fire destroys it. Unfortunately, using fire also causes the lichens to release spores which escape the fire and drift away on the wind. Druidic sects of a particularly malevolent bent gather and cultivate ironrot lichens and use them in their attempts to undermine large population centers. In areas where mining claims are contested, one group may resort to using ironrot lichens as instruments of sabotage.

Section 15: Copyright Notice

Legendary Planet Adventure Path (5E) © 2020, Legendary Games; Authors: Matt Goodall, Jim Groves, Steven T. Helt, Tim Hitchcock, Jason Nelson, Richard Pett, Tom Phillips, Mike Shel, Neil Spicer, Mike D. Welham

This is not the complete section 15 entry - see the full license for this page