The term monster frequency applies to random monsters generation, as opposed to deliberate polymorph results and more specific ways of monster generation. It refers to a number which can technically range 0-7 (though 6 and 7 are not used) used internally to determine how frequently a monster is generated; it can be thought of as a relative probability that a particular monster will be selected.

When a monster is randomly being selected, the game picks a random monster subject to the following list of conditions with relative probabilities equal to the ratios of numberic monster frequencies (thus a monster with a 4 is twice as common as a monster with a 2); this can be thought of as generating a list of monsters with each monster appearing a number of times equal to its monster frequency and choosing purely randomly off of this list.

Randomly generated monsters must be:

  • No greater in difficulty than the average of the level's difficulty and the player level [1]
  • No lower in difficulty than one-sixth that of the current level's difficulty[2]
  • Neither unique nor marked as not randomly generated (G_NOGEN) [3]
  • Not genocided or extinct
  • If you are on the rogue level:
    • Represented by an upper case letter
  • If you are in Gehennom:
  • If you are not in Gehennom:
    • Not marked as only generated in Gehennom (G_HELL) (e.g. hell hound)

Before monster frequencies are used for generation, a number is added to them depending on the relationship between the monster's alignment and the dungeon or special level's alignment. [4]

The following terms are used to describe the frequency of a monster in the infobox on monsters' pages:

Frequency Description
0 Not randomly generated
1 Very rare
2 Quite rare
3 Rare
4 Uncommon
5 Common
6 (unused)
7 Prolific (unused)


  1. makemon.c#line1226
  2. makemon.c#line1246
  3. makemon.c#line1152
  4. makemon.c#align_shift
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