Number of monsters (monstercount) - The maximum number of entities to spawn. 0/-1 = no limit.
Frequency (delay) - Delay, in seconds, between each monster being spawned. If 0, a new monster will only be spawned after the previous has been killed.
Max live children (m_imaxlivechildren) - Maximum number of live children allowed at one time. Spawnings will be suspended until a monster dies. A value of 0 means infinite (obviously not recommended if delay is too low and monstercount is infinite).
Childrens' Name (netname)
Start On (1)
Cyclic (4) - If this is enabled, the entity will activate then deactivate (spawning a single monster) instead of toggling it On/Off when triggered.
Monsterclip (8) - If this is enabled, spawned monsters will not be able to pass through func_monsterclip brushes.
The Flags mechanism for this entity is doped:
If targetname is blank, it will spawn the monster, no matter if "Start On" is enabled or not.
If targetname is named and "Start On" is enabled, the monster will not spawn as soon as the game starts. However, the best way to manage this entity is to give it a name for targetname and set a trigger to activate it (once if Start On is disabled, twice if enabled). Doing so, the mechanics will normalize.
Monstermaker can't spawn active monster_turret nor monster_miniturret, neither spawn a functional monster_osprey nor a properly flying monster_apache since monstermaker can't link a path entity to the target.
Spawning will be interrupted if a monster's hitbox collides with another in-game. Tip: you can use a cycler to render a model on your map editor or insert a monster's typical entity and check its bounding box size.