Mutation Gas (5e Trap)

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Mutation Gas[edit]



This trap is activated by a pressure plate or other activator. The trap can be disarmed with a DC 15 check with thieves tools. On a failure, the trap springs. Once activated, a clear mist is released from a vent somewhere, filling the room and sometimes beyond this. Every turn a creature takes while still in the gas, they must succeed on a DC 15 Constitution check or their cells begin a mutation from the tables below. Each mutation takes D4 turns to complete, and progress each turn. As a DM, you decide appropriate effect for their partial state. A creature that leaves the mist no longer starts new mutations, but will continue any in progress. Any restoration or dispel effect cast with slot 4 or higher will reverse all mutations on a creature (leaves over the time it took to kick in), and if a creature uses a mundane or magic effect to flush out their systems, any mutations they have will filter away over the course of D12 hours - their con bonus. Also, if a creature actively stays in fresh air, eating food, drinking water, and going to the bathroom, their mutations will leave normally over the course of D8 weeks. Tables below!


Effects do not change clothing or gear. Effects do stack and can invert.

1d20 Mutation
1 Gender Swap
2 Increase (turns to complete) sizes, one each turn
3 Decrease (turns to complete) sizes, one each turn
4 Switch race (use a table)
5 Grows wings, flying speed equal to walking speed
6 Become insectoid, shrink down to diminutive and gain wings and other insect parts, flip a coin, heads your still humanoid, tails you are now 6-pedal, its not a complete change, just partial
7 Become part-monster with a monster with CR equal to your level or CR plus con bonus (or minus)
8 Grow spines and claws, unarmed strikes deal D6 slashing/piercing, rips clothing
9 Become a sprite, become tiny and grow wings, gain sprite spells
10 Become Amorphous, can't wear armor and weapons require concentration to hold, gain amorphous traits
11 Become aquatic, gain gills and lose lungs, take D10 fire damage each round if on land, gain swimming speed equal to twice your walking speed
12 Transform into a demon, gain D4, either wings, fire breath, extra limbs, or become non-humanoid, gain demon traits and roll a D4, grow D4 sizes, shrink D4 sizes, stay the same, or become able to choose your size
13 Become polymorphed into a random creature
14 Change appetite, D4, become carnivorous, become herbivorous, become a energy-feeder, or become nutrient-sucking
15 Become formless, have to possess or use other objects (eg. The walls bend to make your body)
16 Flip a coin, heads you grow D6 extra limbs, tails you lose a limb, or D4 if you have more than 4
17 Become elemental, D4, water, fire, air, earth
18 Grow other creatures parts, such as antlers or a tail, or a stinger or web-glands
19 Flip a coin, heads nothing happens, tails you lose a mutation
20 Roll twice, ignore more rolls of 20

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