Impurity
In the context of dNetHack, notdNetHack, and notnotdNetHack, impurity refers to a mechanic that keeps track of tainted or unclean actions performed over the course of the game. It is primarily used by chaotic Undead Hunters and other students of defilement but is kept track of for any character. Impurity is gained either by performing—or being subject to—certain spiritually immoral actions. Whether you are victim or perpetrator does not matter; both are tainted.
Description
There are the 23 categories of exposure, each corresponding to a different set of unclean actions and a corresponding counter that increases every time they are performed. Whenever that counter reaches 1, 4, and 15, that category's impurity score ticks up by one, with most categories allowing at most 3 points of impurity to be gained. When an impure action is performed, there is a 1impurity chance of increasing the current counter, which translates to needing only one exposure for the first point, roughly 7 for the second point, and around 120 exposures for the third.
The "Great Old One transcendence" category instead allows up to 6 points to be gained, with the first three exposures being guaranteed to increment the counter, and subsequent exposures only having a one-in transcendence2 chance of incrementing the counter.
| Odds | |||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Impurity | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 |
| Chance | 100% | 100% | 1⁄2 | 1⁄3 | 1⁄4 | 1⁄5 | 1⁄6 | 1⁄7 | 1⁄8 | 1⁄9 | 1⁄10 | 1⁄11 | 1⁄12 | 1⁄13 | 1⁄14 |
| Odds | |||||||||||||||
| Transcendence | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 |
| Chance | 100% | 100% | 100% | 100% | 1⁄2 | 2⁄5 | 1⁄3 | 2⁄7 | 1⁄4 | 2⁄9 | 1⁄5 | 2⁄11 | 1⁄6 | 2⁄13 | 1⁄7 |
Categories of impurity
| Impurity | Causes | Thresholds (points) |
|---|---|---|
| Meat | Eating meaty corpses: any that would break the vegan and vegetarian conducts count for this. | 1, 4, 15 (3 pts.) |
| Blood | Hitting with—or being hit by—vampiric attacks, quaffing blood, scrawling in blood as a vampire, attacking with the alternate form of the chikage, drawing and transfusing blood. |
1, 4, 15 (3 pts.) |
| Bodies | Picking up corpses, being attacked by skeletons or zombies. | 1, 4, 15 (3 pts.) |
| Death Magic | Using or being hit by death magic or draining magic: wands of death, finger of death, the touch of death monster spell, the drain life spell, and wands of draining. Still applies if you resist or survive. |
1, 4, 15 (3 pts.) |
| Great Old One Transcendence |
Witnessing a Great Old One survive death. | 1, 4, 8, 16, 32, 63 (6 pts.) |
| Theft | Having your items stolen or using stolen items. Stealing a monster's items: natural theft attacks, wages of greed, dolls of stealing. |
1, 4, 15 (3 pts.) |
| Murder | Killing monsters of any type that are both peaceful and intelligent, including, but not limited to, murder. | 1, 4, 15 (3 pts.) |
| Bloodlust | Lowering your alignment record, e.g., reading golden scrolls of law. | 1, 4, 15 (3 pts.) |
| Graverobbery | Digging up graves. | 1, 4, 15 (3 pts.) |
| God Anger | Angering or getting smited by any god. | 1, 4, 15 (3 pts.) |
| Illness | Being affected by severe illness or food poisoning. | 1, 4, 15 (3 pts.) |
| Dirtiness | having the filth spell cast at you, eating filth-crusted items, the effects of a cursed towel. | 1, 4, 15 (3 pts.) |
| Disaster | Being affected by Famine's reach attacks, having any of the following monster spells cast at you: fire pillar, lightning, geyser, acid rain, blood rain, hail flurry, ice storm, and earthquake. |
1, 4, 15 (3 pts.) |
| Seduction | Attacking with—or being hit by—seduction attacks. | 1, 4, 15 (3 pts.) |
| Deep One | Being attacked by a deep one, deeper one, or deepest one. Witnessing Father Dagon or Mother Hydra. |
1, 4, 15 (3 pts.) |
| Betrayal | Being attacked by a pet that has become feral, a traitorous pet, or a befouled wraith. | 1, 4, 15 (3 pts.) |
| Kuo Toa | Being attacked by a kuo toa or a kuo toa whip. | 1, 4, 15 (3 pts.) |
| Ibite | Being attacked by a being of Ib or priest of Ib | 1, 4, 15 (3 pts.) |
| Mind Flayers | Being attacked by illithids. | 1, 4, 15 (3 pts.) |
| Rot | Seeing corpses rot away, binding Ymir, seeing molds grow on corpses, seeing spore zombies revive, being bitten by rot caterpillars or being affected by the spores madness. |
1, 4, 15 (3 pts.) |
| Poison | Hitting with poisoned or dire poison weapons if they trigger the severe effect. Being affected by or attacking with poison monster attacks. |
1, 4, 15 (3 pts.) |
| Curse | Having your items cursed by the curse items spell, being subject to mummy curses. | 1, 4, 15 (3 pts.) |
| Rot Monk | Being hit by rotting monks. | 1, 4, 15 (3 pts.) |
Strategy
For students of defilement, claiming their upgrades requires having at least 3 points of impurity, and 2 additional points of impurity per claimed preservation upgrade and 5 points of impurity per claimed vampiric defilement upgrade. While most categories of impurity can be attained, the "rot monk" and "ibite" categories require interacting with monsters that cannot generate outside their specific quests. For Madmen and Kensei, obtaining impurity in all categories is theoretically possible using bones levels. Most characters will naturally obtain close to 20 impurity over the course of the game. For Undead Hunters who wish to advance their preservation research to the end, there is no need to go out of their way to increase their impurity right away. Vampire defilement researchers will want to check off the easier impurity categories once they start being able to claim their upgrades and make liberal use of the easier impurity categories such as "filth", "blood", "graverobbing", "bodies" and "murder".
Origins
Impurity is inspired by the Shinto concept of Kegare, representing how tainted you are by your actions and the things that have happened to you. As you accumulate impurity, certain blood-related effects become more potent, as well as a few other small effects.
