I dont know what cost_mult does, but it defnitely has something to do with noise and monster density. My guess it that you could assume that each unit is tracked by the game, and the more ire you attract, either through noise for zoms, or by killing ants outside their hill or by walking over fungus’ tendrils area, the more points go into a pool that monsters draw from to spawn. So large and dagerous groups of monsters, say 1 hulk or a group of 50 zombies, will pull more resources, while a lone child zom pulls less. Obviously in addition to frequency, cost_mult limits the occurance of a hulk because there might not be 50 units in this system.
Frequency is a direct weight. The game assigns 1 lot per number n freq. So a hulk gets 1 lot for having 1 freq. But runners have 20 freq, iirc. So 1-4 runners get 20 lots.
The game tallies up all the lots and picks one, and then places that critter somewhere if it can afford to because it has more ‘cost_mult’ than is needed to do so. Its all statistcs.
-Because this is the case, adding new groups will upset the ratios, and you should keep that in mind when playing with numbers.
I have no clue what happens if it pulls a hulk but cant spawn it because it doesnt have enough ‘cost_mult’
