You wanna allow some mob spawning after player reach some game progress, similar to Terraria? Now it's possible with this mod. You can easily make it just by using config file.

Here is example of rules

[
  {
    "example": true, //delete this value or make it false to apply rule
    "entities": ["minecraft:zombie", "minecraft:zombie_villager", "minecraft:husk"],
    "achievement": "minecraft:story/enter_the_nether",
    "messages": {
      "en_us": ["Now zombies arise in the dark", "Beware of the night!"],
      "uk_ua": ["Тепер зомбі з'являються в темряві", "Остерігайтесь ночі!"]
    },
    "messagesColor": "GOLD"
  },
  {
    "entities": [...],
    "achievement": "...",
    "messages": {
      ...
    },
    "messagesColor": "..."
  }
]

Here you can find all achievements to configure

Here colors for chat message

Update

With new update now you can block entity to spawn with another config file block-after-achievement.json

!!! Important

"messagesColor" is white by default,

"messages" let you set few messages that will displaced accidentally,

Both parameters "messages" and "messagesColor" are not required

Set "example" to false or delete it to make rule work

I recommend to check all the config files of this mod

The most delicious that it's fully works with any entity from another mod
Nerkin