Monsters (by difficulty)
A monster's difficulty (also known as its MONSTR) is a number from 1 to 57 which represents the game's idea of how tough a monster is. It is based on the monster's level, then adjusted (see below) for any special properties the monster has which might make it extra-difficult. The raw values can be seen in monstr.c.
A monster is "too strong" to be randomly generated when its difficulty is greater than the average of your experience level and your dungeon level. It is "too weak" to be randomly generated when its difficulty is less than your dungeon level divided by 6, rounded down. (For this purpose, once you have the Amulet of Yendor your dungeon level is considered to be that of the Sanctum, and in the endgame to be the depth of the Sanctum plus half your experience level.)
The level of your god's appreciation of a sacrificed corpse is also dependent on the corpse's Difficulty (and not on the late monster's experience level). If your god is angry, you must sacrifice a monster corpse of difficulty 7 (11 if you are chaotic) or greater in order to mollify the god.
Most of the less common mechanisms of monster generation do not have similar limits.
If the monster's base level is greater than 49 (meaning that it's either a mail daemon or a demon lord), instead set the initial difficulty to (base level - 6) / 2.
Next, compute a bonus based on properties of this monster:
- Start at 0.
- Add 1 if the monster generates in small groups.
- Add 2 if the monster generates in large groups.
- Add 1 if the monster is capable of ranged attacks: whether it has any weapon, spellcasting, gaze, spit, or breath attacks.
- Add 1 if the monster's base AC is between 0 and 3, inclusive.
- Otherwise add 2 if the monster's base AC is -1 or lower.
- Add 1 if the monster's speed is 18 or higher.
- For each attack the monster has, add together all the following bonuses:
- Add 1 if the attack is non-passive.
- Add 1 if the attack is arcane spellcasting (AT_MAGC).
- Add 1 if the monster is strong and the attack is a weapon attack (AT_WEAP).
- Add 2 if the attack has a damage type of AD_DRLI (drain life), AD_STON (stoning), AD_DRST (strength poison), AD_DRDX (dexterity poison), AD_DRCO (consitution poison), or AD_WERE (lycanthropy).
- Add 1 if the damage type is none of the above six types and is also not AD_PHYS (physical damage), and the monster is not a grid bug.
- Add 1 if the maximum attack damage for this attack is 24 or higher.
- Subtract 2 if the monster is a leprechaun.
Then, modify difficulty based on what the bonus worked out to be:
- If the total bonus equals 0, subtract 1 from difficulty.
- If the total bonus is 6 or higher, add half of the bonus, rounded down, to difficulty.
- Otherwise, if the total bonus is between 1 and 5, add 1 + one-third of the bonus, rounded down, to difficulty.
Finally, if difficulty is negative (only possible with very weak monsters like lichens), set it to 0.
This table was generated with the use of a modified version of makedefs to calculate experience values as well, and is believed by the author to be accurate. If there are discrepancies between these and those listed in the articles, please correct the article.
- util/makedefs.c in NetHack 3.6.0, line 2117
- util/makedefs.c in NetHack 3.6.0, line 2156: This is evidently to compensate for leprechauns' base level being artificially inflated, and to cancel out the 2 points they get from their gold-stealing attack. It is unclear why the bonus is not simply set to 0 here.
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