Monster Generation

Each monster has a minimum dlevel, a maximum dlevel, a weight, and a danger rating. Minimum level and maximum level determine whether the monster can appear on a floor at all. Weight indicates relative likelihood of appearing. Danger indicates (inversely) how many can be generated.

The displayed minimum level is valid for ITYTD and HNTR, and it is smaller at higher difficulties (-3 for HMP and -6 for UV/N!), which means that tougher monsters start appearing earlier in the game. Other values are unaffected by difficulty.

For the more all enemies that can normally spawn, here are the values.

Additionally, the are monster groups. Monsters groups have their own minimum and maximum levels and weights that are used instead of the values for the the individual monsters. The effective danger of a group is the sum of the dangers of its monsters.

Notice that monster groups are the only way for some enemies to appear on very deep levels.

Each level is given a total danger rating depending on depth and difficulty level. Monster placement usually proceeds as follows: while the total danger of enemies placed so far is less than the danger rating of the level, pick a new monster or monster group and add it (entirely) to the level. Picking a monster or group is done using the weights as relative probabilities for all the monsters and groups with a valid dlevel range. When a monster group is picked, all its ranges are resolved uniformly and independently. Each monster is added to a random empty tile; for monster groups, each monster is added separately.

The total danger level is calculated from dlevel as follows:

In addition to these monsters, certain level features (e.g. vaults) may cause additional monsters to spawn on the level without counting against this limit.