Radiation Elemental & Radiation Poisoning – Horrors of the Post-Apocalypse for D&D 5th Edition

Elemental, Radiation

“A horrific visage emerges from what looks like a nuclear bomb blast!  The image of a skull begins to manifest within a mushroom cloud as the explosion seems to have gained the ability to travel!  The ghoulish form begins to gain on you as geiger counters begin to spin out of control.  In a flash of green light, your horse mount collapses in a frantic twitching fit as the living embodiment of the apocalypse has come to claim you!”


The truth behind elementals of radiation is a mystery.  Countless theories have cropped up throughout the multiverse!  One states that a technologically advanced society was testing all sorts of weaponry on the elemental planes.  Amidst the devastation caused by the weapons, a new elemental demiplane was created as a result.  A more insidious rumor comes from the fiendish mercenaries of the Blood War, the Yugoloths.  According to the more knowledgeable in outer planar lore, arcanoloths have mastered the arts of time and dimensional magic.  Amidst their travels, they witnessed an entire nation being nearly wiped out by two missile like weapons.  Intrigued by this capacity for evil, they tried to replicate this power into their own engines of hatred and war.  Their result was an elemental being so corrupted, it holds malice for all living beings; a testament to daemon manifesto!  However, both of these theories lack evidence to back them up.  In the meantime, we can only hope some addle-cove doesn’t try to conjure one of their own upon the material plane!

Radiation Elemental

Large elemental, neutral evil


Armor Class. 15 (natural armor)

Hit Points. 102 (12d10+36)

Speed. 40 ft. fly 40 ft. (hover)


STR – 15 (+2), DEX – 18 (+4), CON 17 (+3), INT 6 (-2), WIS 10 (+0), CHA 7 (-2)


Damage Resistances.  acid, cold; bludgeoning, piercing, and slashing from nonmagical weapons

Damage Immunities.  necrotic, poison, radiant

Condition Immunities.  exhaustion, grappled, paralyzed, petrified, poisoned, prone, restrained, unconscious

Senses.  darkvision 60 ft., passive Perception 10

Languages.  Primordial (??)

Challenge.  7 (2,900 XP)


Dust of Decay.  The elemental can enter a hostile creature’s space and stop there.  It can move through a space as narrow as 1 inch wide without squeezing.  Any creature caught within the path of this creature is effectively blinded.  Any area 30 ft. around it is considered mildly irradiated.  Since it is heavily concentrated radiation, targets must make a saving throw (DC 10) at the start of their turn each round.

Cosmic Indifference.  Despite being an animated embodiment of entropy, it cares not for what it encounters.  While it takes sadistic joy in irradiating its prey to death, it doesn’t seem to be too phased by their escape.  This creature will not take reactions to make attacks of opportunity.


Multiattack.  The elemental can make two slam attacks.  Alternatively, it can make a slam attack and attempt Nuclear Storm.

Slam.  Melee Weapon Attack: +8 to hit, reach 5 ft., one target.  Hit: 16 (3d6+4) radiation damage

Nuclear Storm.  (Recharge 5 or 6)  As an action, the elemental can increase the power of their “Dust of Decay ability” from mild radiation to moderate radiation.  This lasts 1d4 rounds.



New Rule – Radiation

Radioactive power has the capacity to both run a civilization and destroy it.  When its used to bring entire landscapes to utter ruin, it also succeeds in scarring the landscape.  Irradiated areas are among the most treacherous and tainted in existence.  Just as potent as the strongest dark magic, radiation corrupts and decays all it touches.  When in an irradiated zone, characters must roll Constitution saving throws to avoid becoming potentially ill.  Players usually begin rolling checks after 1 minute of exposure and continue to do so every minute.  When engaged within combat, players are more focused on enemies, leaving them more open to the hazardous terrain.  In this case, players must make saving throws every 1d4 rounds.  If radiation is increased or decreased in level, simply alter the amount of damage given on a failed save.

Radiation Damage.  While simply using necrotic and radiant works for some, it won’t suffice for me.  As such, radiation counts as a damage type.  Essentially, it works like a mixture of the two for weakness and resistance.  Upon taking Radiation damage, the target must roll a Constitution saving throw based on the amount of radiation they were exposed to.

Characters who are resistant to radiation damage also have advantage on saves versus radiation (Constitution save).  Characters who are immune to radiation damage are also immune to radiation poisoning.  Necrotic or radiant resistance also count for the advantage bonus.  However, in order to gain immunity in this case, you must be immune to both types.

Table: Radiation Damage Severity (Counts as 1 round of being in Irradiated Area)
Total Radiation Damage Taken during Round Radiation Exposure (Immediate Saving Throw)
1 – 8 Mild
9 – 17 Mild
18 – 26 Low
27 – 35 Low
36 + Moderate
Table: Radiation Sickness
Exposure Constitution Saving Throw DC Resulting Damage
Mild 10 1 Level Exhaustion
Low 14 2 Levels Exhaustion
Moderate 18 3 Levels Exhaustion
High 22 4 Levels Exhaustion
Severe 26 5 Levels Exhaustion

Campaign Option: Prolonged Environment Exposure – To add a more realistic approach, radiation might have a more latent effect on the victim.  Depending on how long also depends how severe of an infection could be.  This assumes the radiation is in a spread out area that on average stays at a level of radiation.

Table: Time in An Irradiated Area
Level 1 round 1 minute 10 minutes 1 hour 1 day
Light Radiation mild mild mild mild low
Moderate Radiation mild mild low low moderate
High Radiation low low moderate moderate high
Severe Radiation moderate moderate high high severe

Incubation for after preliminary radiation exposure – 1 Round = 1 Day, 1 Minute = 4d6 hours, 10 Minutes = 3d6 hours, 1 Hour = 2d6 hours, 1 Day = 1d6 hours

Campaign Option:  Fallout-Style Radiation – In this module, we assume you’re running a game closer to Fallout.  Either that or you aren’t a huge fan of the D20 Modern style radiation tables.  In this module, radiation checks are based on frequency to simulate how intense the radiation is.  Instead of rising levels of exhaustion for higher levels, the player simply rolls saves more often.  Failure results in 1 level of exhaustion.  When in combat, engaged against a radioactive creature; the character must also save based on the level the creature gives off.

Level of Radiation in Area – Save Frequency

Light Radiation –                 Once every 2d6 rounds (1 minute – 10 rounds)

Moderate Radiation –          Once every 1d6 rounds (1/2 minute – 5 rounds)

High Radiation –                  Once every 1d3* rounds (1/4 minute – 2 / 3 rounds)

Severe Radiation –              1 round

*1/6 divided by 2, round up (1 – 2 = 1; 3 – 4 = 2; 5 – 6 =3)

Monstrous Radiation (How radioactive the monster is) – Save Frequency (This form of radiation is considerably more concentrated and thus more deadly)

Light Radiation –                Once every 1d8 rounds (1/2 minute)

Moderate Radiation –         Once every 1d4 rounds  (1/4 minute)

High Radiation –                 Once every 1d2 rounds (Every other round)

Severe Radiation –             Every time attacked by Radiation damage

Campaign Option: Medical Treatment – Due to the harsh power of radiation, afflicted require intensive treatment.  Under normal circumstance, these infections will not go away with rest.  During a long rest, someone trained in Medicine or in a healing kit can attempt to help a victim recover from 1 level of exhaustion (DC 20).  However, Greater Restoration helps remove a level of radiation poisoning as well.  Failure results in treatment being ineffective for that period.  This cannot be tried again during the remainder of that rest.  Alternatively, an Auto-Surgeon can provide treatment for you, often at a cost for its services.  More on Auto-Surgeons here.

Campaign Option:  Mutation – In addition to saving versus radiation, exposure could result in mutations.  Depending on how well the character saved on the radiation check will also result in how likely they are to get a positive or negative mutation.  If they succeeded a check by 10 or above, they receive no mutation.  If they succeed by 0 through 10, they receive a positive mutation, same if they fail by -1 through -4.  If they fail by 5 or more, they receive a negative mutation.  Mutation rules are found here and here

Tables inspired by D20 Apocalypse and Dungeon Musing’s conversion of Iron Gods for D&D 5e.

Created by Doctor Necrotic for Doctor Necrotic Media.  Based off the D20 Modern and Pathfinder Roleplaying Games by Wizards of the Coast and Paizo respectively.


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