Hexen scripted monster spawning
Hexen and its expansion set both feature levels that must be visited several times and a gameplay focused on searching for multiple keys and switches. To prevent a map from becoming too empty in a latter visit, as well as to incite the player to move forward and progress, most maps feature a monster repopulation script in slot 255.
The repopulation scripts in Hexen are run every 8400 tics (four minutes). Each spot has a 50% chance of spawning its associated monster.
Deathkings of the Dark Citadel
The repopulation scripts in Deathkings are more advanced. In cooperative mode, they only delay by 4200 tics (two minutes). Usually, they choose one monster type randomly in a first step (usually from three types with a 60%/30%/10% distribution), and then each spot has a 50% chance of spawning this monster. However, some maps spots are still exclusive to one type of monsters; if so they are listed separately.
† The single-player delay is only 6300 tics (three minutes) in this level, instead of 8400 tics as usual. Cooperative delay is still 4200 tics.
‡ The single-player delay is 10500 tics (five minutes) in this level. Cooperative delay is 6300 tics.
◊ This level uses Thing_SpawnNoFog instead of Thing_Spawn.