Burn Baby Burn: Simplified Immolation Rule

"Fire is a burning thing..."

A simple and consistent rule for adjudicating when something is set on fire:

If a creature or flammable object takes fire damage ≥4 it is set on fire. 

• While on fire, it takes d4 fire damage at the end of each of its turns (or the round if it doesn't have a turn), if the damage is ≥4 it continues to burn.
• If a creature is doused with oil or some other accelerant, they'll take d6 instead of d4 and are consequently much more likely to keep burning for multiple rounds.
• Taking a turn to stop, drop and roll will put out the fire on humanoids but may not work on especially flammable creatures (e.g. a scarecrow).

Some implications: 

Torches: Usually, the torch is passed off to a hireling or underpowered PC so that they can stand near the back in safety. No more! 

• Torches deal 1d4 fire damage. If they roll a 1 for damage they go out, if they roll a 4 for damage, they set the target on fire (assuming it is flammable to begin with). 
• Torches are great vs. a range of threats: Scarecrows, mummies, paper-golems and twig blights. Things with fire vulnerabilities are almost certain to be ignited and will burn up quickly. Furthermore, in my game Shadows, Specters, Phantoms and other incorporeal monsters made of darkness take damage from fire but not from most mundane weapons.

Darkest Dungeon

Molotov Cocktails: Throwing flasks of burning oil is a D&D classic. 

• A burning oil flask deals 1d6 damage to creatures in a ~5' radius. Usually, 2-3 creatures if closely grouped. 

Magic Mirrors

Disney's Snow White

Magic mirrors are a common trope in myth and fantasy.  Across history and around the world, people have seen mirrors as possessing supernatural power, from Vulcan to Tezcatlipoca.

Trying to tap into that mythic resonance, I've come up with several mirrors to stock dungeons: 

1. Paralyzing Mirror - This mirror instantly paralyzes anyone who can see any part of their own reflection in it. Escape requires help from someone who avoids looking at their reflection.
2. Window Mirror - This mirror shows whatever is on the other side of the wall on which it is hung as if it were a window.
3. Ghost Mirror - This mirror shows ghosts in its reflection. 
4. Spell Mirror - If any magic user peers into this mirror for one minute, they memorize a single use of the Mirror Image spell (in addition to any other spells they have memorized). If the spell has not been cast by the time the mage sleeps, it fades away. 
5. Extra Object Mirror -  This mirror shows an object (perhaps a vase etc.) not present in the real world. Finding the object and placing it to match its position in the reflection will unlock a secret door to another part of the dungeon. 
6. Broken Mirror - One shattered piece is missing (hidden elsewhere in the dungeon) but if the mirror is reassembled, a floating face appears and will answer any one question for each person that stands before it. 
7. Reflecting Pond - The surface of this small pool is agitated by a large and active fish that darts about in the water. If the fish is removed or stilled, the water will settle and show scenes of the distant past. 
8. Paired Mirrors - If the scenes reflected in these two mirrors match (aside from any living things) a person can step into one mirror and out of the other like a magic portal.  

Still Snow White

Monster/Hazard: Powder Moth

 

Under the earth, beyond the reach of the sun's rays, where light is precious and maintaining torches and lanterns is a matter of life and death, the powder moth is a fearsome pestilence. 

Mothra

By the standards of terrestrial moths (of the sort well known to surface-dwellers), powder moths are enormous*. Fully grown, each is the size of a mid-sized dog with a wingspan wider than a man's outstretched arms. 

Powder moths are drawn ineluctably to light and if they come into direct contact with open flame they explode violently. 

Powder Moth

Armor Class: 8 (unarmored)

Hit Dice: 1-1 (HP2)

Attacks: None, see Special

Move: Fly x2 speed of unencumbered human

Saves: 15+

Morale: Drawn to light, avoids all other contact

Number Appearing: 1d6

Treasure: Corpse is worth 100GP to an alchemist.

Special: Drawn to any light source and explodes on contact with open flame dealing d6 blast damage to all creatures in immediate proximity. Enclosed flames (e.g. glass lantern) won't detonate moths but moths will collide with the light source repeatedly.

___

Powder moths infest subterranean areas and feed on Yellow Mold (a la AD&D Monster Manual). 

Although they are reviled by torchbearers and linkboys, delvers often hesitate to exterminate populations of moths because their removal typically results in rapid fungal expansion. 

The wings of dead moths can be carefully ground to produce a black powder used in the production of grenades and as propellant for cannons. It is rumored that the Imperial legions farm powder moths in depleted mines to supply their artillery. 

bowelfly on tumblr

*Powder moths (and other large chthonic moths) are dwarfed by the truly titanic moths that live in the outer void, with bodies large enough to host cities.

Discussion

I've been trying to come up with some unique low-level monsters for my wandering monster tables. I want adversaries that are hazard/challenges rather than just HP piles to chop through. 

The presence of powder moths adds a layer of consideration (the ever-popular torch & molotov load-out becomes a risky move) that should make an area feel distinct.

The first time these are encountered they'll be a real threat. Explosion followed by darkness. 

Once the party has figured out a strategy to defeat them, they become a resource rather than a danger. I can imagine all sorts of PC schemes to hunt moths for their explosive potential.