There's mods that changes the spawning paramenters, but this ones shouldn't affect to ice&fire creatures, cause thoose are not naturally spawned, they're spawned with the structures instead.
Rats mod have a low chance to spawn rats if you didn't make a garbage field, but thinking about it.
The both mods that you mentioned gives an archievement to the player first time he joins the world.
If you didn't read of the chat any of the archivements, then the mods are just not loaded.
Possible reasons in case the mods are not loaded:
- You didn't installed forge or not running minecraft with forge
- You didn't placed the mods in the mod folder
- The version of your mod files is not for the version of your forge
- You placed the mods into mods folder, but forge istance have a diferent path, so is looking on another folder still empty
- The files doesn't have .jar extension
- The files are compresed in .zip or .rar
- You think you downloaded that mods, but you download them for a random weird site and its a fake file.
How to NEVER have problems like this while installing mods? Using the aplication of curseforge.
Its really easy to use, allows you to create different instances in different versions with diferent mods and took like 5 minutes to get ready a working minecraft custom modpack without this kind of problems that you have now.
That sounds like some of the config files had weird information that the mod can't read properly, but if that was the case, the game should have sended some kind of error message instead of running without the mods.
Do you have instaled any other mod that can affect to the world spawning?
For example, on 1.12 there's a mod called "biomeTweaker" that changes the mob spawning on each biome, that mod autoupdates the spawnlist when you add more mods cause only saves your custom settings. But any other mod that makes something similar and doesn't have the custom config separated from the original one, can cause this.
Can I see what other mods did you installed to figure out why does that happened to you?
Makes sense, that modpack have several issues in more than one way.
But actually on that aspect, I think that then it WASN'T an error, cause modpacks usually use mods to control and customize mob spawning.
That's... why they're made. The configuration that you deleted is the configuration that the modpack creators wanted.
Last time I tried that modpack, plague doctors spawn, but rats doesn't like the mod usually do. To get rats you have to craft a trashcan and make a place for them to spawn.
So right now, you're no longer playing ATM6, you just using the same mods.
So... yeah, for now on you can't blame lack of content and archivements on the modpack cause all of that is on the folders that you deleted.
This settings are usually made for balancing and giving the player a better experience.
Also, if I can do a recomendation, if you doesn't want that the modpack creators decide the game for you, you should choose the mods by sourself.
Just cause that modpacks adds A LOT of mods that most of the players didn't even use and sometimes didn't event like. So that not only ruins you're game experience, also gives you a lot of unnecessary lag...