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Gloomium (Radiation)

One of the other things I don’t like about the Iron God Adventure Path is the extensive use of scientific terms.  I do my best to avoid this and rename things more appropriately   Nimmerians don’t use the word radiation, for example, as this is a scientific term.  Though the locals are well aware of its lethality and refer to the effects as the Phantom Death.  For convenience, I usually just call it what it is – radiation poisoning – around the gaming table.  
Credit to Fallout for the name and the WoTC DM forum members who gave me the idea to use exhaustion (5e) as a mechanic to replace Ability Drain (3.5e). 
Glomium = is a uranium like substance that glows green in my world. Name stolen from the Middenlands RPG.


Each character starts with a radiation die (d8), construct lifeforms have no radiation die as they are immune to poison and radiation.  This die increases to d10 for mutants and rad sorcerers. When you approach a zone that is glowing from radiation, roll your Radiation Die.

Depending on how close you are to the source of the glow and the level of radiation, roll more or less often:

  • Low, 1/day,
  • Moderate 1/hour,
  • High 1/minute,
  • Extreme 1/round.

Each time you roll a 1-2 on your radiation die reduce the die type (d20 > d12 > d10 > d8 > d6 > d4) and take 1 level of exhaustion for each step the radiation die has decreased from its original size. If you roll 1-2 on a radiation die the size of a d4, roll a d6 on the table below.

The radiation die never goes below d4, but a roll on 1-2 still counts as if it was reduced and you automatically gain a random mutation – roll a 1d1000 and consult the Metamorphica. The maximum number of mutations a creature can have is 5, becoming an inhuman, drooling, monster once the 6th mutation is gained.

Certain arcana and magic mitigate the effects of radiation. Any magical effects that gets rid of exhaustion levels can increase your radiation die by 1 step up to its normal maximum.  Other arcana can also restore your radiation die – for example, potion of vitality, and greater restoration refreshes the Radiation Die by one step, up to its maximum.

At lower levels protection from poison can be used to increase the die.  This does not work automatically on radiation poisoning – the caster must make a spell check against DC 25 if they succeed they immediately refresh the Radiation Die by one step, up to its maximum.  If they fail they must spend a week ministering to the creature with radiation poisoning to refresh the die.  No other strenuous activities can occur during this time and the poisoned creature is bedridden as well.


Radiation can be naturally or artificially produced. All stars produce radiation in some variety, and planets closer to these stars typically suffer more severe effects than worlds farther away. Many starships and other pieces of technology incorporate radioactive parts and fuel cells that can flood an area with harmful radiation when ruptured or exposed. Ancient alien civilizations might leave behind powerful artifacts that emit harmful radiation. Whether the source of the radiation is natural or artificial, any character in an environment rich with radiation may suffer some negative effects for exposure.
Radiation is a cScreen Shot 2015-02-26 at 23.08.04ontact poison effect the severity of the exposure determines the lethality of the dose (and the DC).  Creatures that are exposed to radiation must make a Constitution saving throw each round or suffer levels of exhaustion, as set out in the Radiation Damage table.
Radiation is poison damage and any ability or spell that affects poison will, likewise, affect radiation damage.  Creatures that are immune to poison damage take no damage from radiation, and creatures resistant to poison damage reduce the strength of the effect by one step. For example, one level of exhaustion would become poison status effect.


Radiation is a new damage type which is a powerful form of poison damage. When a creature does radiation damage treat it as poison damage with the following additions:

  • If a save triggered by the radiation attack the creature also gains 1 level of exhaustion when it takes damage from the attack.
  • If a creature is hit by the attack – even if no damage is taken – the attack strips away poison resistance by one step for the rest of the encounter. This will eventually make the target vulnerable to poison damage. This occurs before applying damage. For example, a green dragon which is immune to poison damage hit by radiation would have its immunity reduced to resistance. If it is hit again by a radiation attack the green dragon would lose its resistance to poison. Another hit from radiation damage would make it vulnerable to poison damage.
  • A creature that rolls a natural 1 on a saving throw triggered by a radiation attack is mutated.
  • A creature reduced to 0 hit points is dead and turns to ash and all that is left is a morbid shadow burned into the floor where it died.
Posted in 5e, Adventurer's Vault, Iron Gods, Science-Fantasy, The Ninth World


  1. solomani

    update 23022019: After playing with this mechanic for 4 years I ended up making radiation a special poison damage type. See below. I didn’t want high-level characters who are pretty much immune to poison by the mid-teens to no be threatened by radiation as its intrinsic to my campaign setting. But I also didn’t want to take away anything earned by the PCs like heroes feast. Compromise below.

  2. solomani

    Removed 1d6 table and just went straight to rolling a 1d1000 and consulting the Metamorphica.  

  3. solomani

    Made explicit mention of potion of vitality, protection from poison, and greater restoration as ways to refresh the Radiation Die.

  4. solomani

    Added a limit to the number of mutations: “The maximum number of mutations a creature can have is 5, becoming a inhuman monster once the 6th mutation is gained.”

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