Mob Stages Mod 1.12.2 is an add-on for the GameStage API. Mobs’ spawning in the game is currently available to appear in a custom progression system.
Mob Stages

To learn more about the mod, please visit the GameStage API mod’s description!
Stages
They are parts of the progression program. They are established by the mod pack or the server.
They belong to the player through a command, which is often managed by a questing mod, advancements, or a command block.
Setups
The release chooses CraftTweaker for configuration.
Global
mods.MobStages.addStage(String stage, String entityId): adds a mob to a level.
mods.MobStages.addReplacement(String entityId, String replacementId): supplements an alternative
mods.MobStages.addRange(String entityId, int range): creates the range to seek out players
mods.MobStages.toggleSpawners(String entityId, boolean allow): helps mob spawners skip the stage rules and spawn the creature
Dimensional
Have various variants of the methods in the first section. They obtain the dimension ID as an additional last parameter.
Mob Stages is a server utility mod, an addon for GameStage API. To unlock its content, please install Minecraft Forge!
How to install Mob Stages Mod:
Assure that you have already installed Minecraft Forge
Define the location of the Minecraft application folder.
On the windows, open Run from the Start Menu, write %appdata% and click to Run
Open Mac on the finder, press and hold Alt and click to Library on the peak of the Menu Bar. Open the Application Support directory and look for Minecraft.
Put Mob Stages Mod you have already downloaded (.jar) into Mods directory.
When you start using Minecraft, open the mod button, you will realize that Mob Stages Mod has been set up.
Screenshots