Side note to that, seems some of the NPC packs spawn far more frequently than others. Not all that many NPCs spawning vs the zombies etc. Not seeing an option to change ratios, does that exist somewhere?
This is a very good point and something Addon creators will be given more guidance on as things move forward.
These settings are governed independently by the Addon creators, with the NPCMod acting as base for them to be powered by, but guidance is clearly essential to ensure parity when multiple Addon Packs are installed.
While things are being set up and stabilised, it has been a bit of a free for all with one pack setting higher spawn rates than another. This makes it rather futile to combine Addon Packs if one is not going to spawn. Some guidance for Addon Pack creators is just being worked out in order to find an optimal balance. This will be based on a hierarchy of spawn rates to modulate appearances, and one possible candidate is as follows:
Default Settings (which can naturally be changed by Server Admin/Host to suit their own game play styles)
1. Standard zombies will always have the highest spawn chance out in the Biomes and take priority. Typically 100% chance.
2. Non standard zombies will have the second highest chance to spawn out in the Biomes. Typically 5% to 50% chance.
3. Then comes the NPCMod Addon Packs which should be lower than the lowest non standard zombie. They have a chance of 2.5% to 10%.
These are all dependent on the Biome as well.
For example, these are some of the most important Biome spawning zombie groups which the NPC are also added to:
All Zombies - The Janitor Zombie is the lowest Vanilla spawner with a 20% chance to appear.
Night Zombies - The Zombie Dog is the lowest Vanilla spawner with a 5% chance to appear.
Snow Zombies - The Feral Lumberjack Zombie has a 10% chance to appear. (There are also some separate game stage considerations for the snow biome)
Wasteland Zombies - All Vanilla spawners have a 100% chance to spawn with some being given even more chance.
Wasteland Night Zombies - All Vanilla spawners have a 100% chance to spawn with some being given even more chance. In addition, spawning frequency is much higher as we all well know if we venture into the Wasteland Biome 'alone' at night.
If there are too many NPCs, then the regular zombies will be wiped out too quickly and probability eventually says they will ultimately be replaced by another NPC. This can create a sterile World. But if there are too few NPCs then it will take some time for their numbers to increase. And as you are seeing, if one Addon Pack allows a high spawn chance (compared to other NPCs and zombies) then it can upset the Biomes.
It is a delicate balancing act, but it is being addressed.
It will also require a level of compliance from Addon creators to ensure all Addon Packs are given a fair and equal chance to appear in the World by default.
If you want to share what you have installed, and what you would like to see, then provide the details and we can advise you on a one setting fits all that can be added to all of the packs you have installed. It may take a little time for you to edit the entitygroups.xml for each but you'll always have those as templates. It will also help us see if the candidate settings are working out in the wild based on your future feedback.