Dimension Authority
This is a Mod that lets you cut off access to the dimensions you don't want entities going to.
In the Dimension Authority Mod, you will be able to use commands (as an operator) to lock/unlock dimensions. When a Dimension is locked, players will not be able to enter that dimension.
Commands:
/lockEnd : Makes players unable to go to the end
/unlockEnd : Makes players able to go to the end
/lockNether : Makes players unable to go to the nether
/unlockNether : Makes players able to go to the nether
/lockOverworld : Makes players unable to go to the overworld
/unlockOverworld : Makes players able to go to the overworld
The Dimension Authority Team
