Illusion is a rewrite of FibLib. It allows you to lie to clients about BlockStates being sent to clients based off player predicates. Take this example...

Prevent a player from finding Iron Ore while they are sneaking.

var illusion = Illusion.create()
        .map(Illusion.from(Blocks.IRON_ORE), Illusion.to(Blocks.STONE))
        .modifyDrops(true)
        .modifyProperties(true)
        .when(Entity::isSneaking)
        .build();

IllusionRegistry.register(illusion);

This Illusion will remap Iron Ore to Stone on clients when they are sneaking. Iron Ore will still exist on the server, but any interactions will act as if the player interacted with stone - including block breaking speed, block drops, and more.

Illusion is available on the Draylar maven:

maven {  
   name = "maven.draylar.dev"  
   url "https://maven.draylar.dev/releases"  
}

// For Fabric developers:
modImplementation "dev.draylar:illusion-fabric:${project.illusion_version}"

// For Forge developers:
modImplementation "dev.draylar:illusion-forge:${project.illusion_version}"