For instance, i want that Husks can spawn inside the Desert Pyramid like Wither Skeletons does in the Nether Fortress. But i've tried using the InitMapGenEvent but in the EventType there's nothing that can lead to the pyramid (while instead there is the NETHER_BRIDGE type that lead to Wither Skeleton spawn). So how can i force the game to spawn an entity in a specific structure (in this case a Husk in a Pyramid)?

Thank you for the answer but i did not understand how to get the Chunk Provider since if i do event.getWorld().getChunkProvider() then i can't access to chunkGenerator field

Ok, so i got this right now

@SubscribeEvent
public void onTerrainGen(WorldEvent.PotentialSpawns event) {
	if(event.getWorld().provider instanceof WorldProviderSurface) {
		ChunkProviderOverworld chunkGenerator = (ChunkProviderOverworld) ((WorldServer)event.getWorld()).getChunkProvider().chunkGenerator;
		MapGenScatteredFeature map;
		Field[] fields = ChunkProviderOverworld.class.getFields();
		for (Field element : fields)
			try {
				if (element.get(ChunkProviderOverworld.class) != null) {
					if (element.getName().equals("scatteredFeatureGenerator")) {
						map = (MapGenScatteredFeature)element.get(ChunkProviderOverworld.class);
						break;
					}
				}
			} catch (IllegalArgumentException e) {
				System.err.println("Illegal argument passed as Block to register");
				e.printStackTrace();
			} catch (IllegalAccessException e) {
				System.err.println("Illegal access while registering a Block");
				e.printStackTrace();
			}

		StructureStart structurestart = map.getStructureAt(event.getPos());

        if (structurestart != null && structurestart instanceof MapGenScatteredFeature.Start && !structurestart.getComponents().isEmpty())
        {
            StructureComponent structurecomponent = (StructureComponent)structurestart.getComponents().get(0);
            if(structurecomponent instanceof ComponentScatteredFeaturePieces.DesertPyramid) {
            	event.getList().add(new SpawnListEntry(EntityZombie.class, 20, 1, 3));
            }
        }
	}
}

 

But when i do this

StructureStart structurestart = map.getStructureAt(event.getPos());

it gives me an error telling me that getStructureAt is not visible. How can i solve this?

I never used reflection so i could make some mistakes. However i now have this, no errors are given but is this correct or again something is wrong?

if(event.getWorld().provider instanceof WorldProviderSurface) {
		ChunkProviderOverworld chunkGenerator = (ChunkProviderOverworld) ((WorldServer)event.getWorld()).getChunkProvider().chunkGenerator;

		Field mapGen = ReflectionHelper.findField(ChunkProviderOverworld.class, "scatteredFeatureGenerator");
		mapGen.setAccessible(true);

		MapGenScatteredFeature map = (MapGenScatteredFeature)mapGen.get(ChunkProviderOverworld.class);

		Method getStructure = MapGenScatteredFeature.class.getDeclaredMethod("getStructureAt", MapGenScatteredFeature.class);
		getStructure.setAccessible(true);

		StructureStart structurestart = (StructureStart) getStructure.invoke(event.getPos());

        if (structurestart != null && structurestart instanceof MapGenScatteredFeature.Start && !structurestart.getComponents().isEmpty())
        {
            StructureComponent structurecomponent = (StructureComponent)structurestart.getComponents().get(0);
            if(structurecomponent instanceof ComponentScatteredFeaturePieces.DesertPyramid) {
            	event.getList().add(new SpawnListEntry(EntityZombie.class, 20, 1, 3));
            }
        }
	}

Ok, i will check it out and hopefully managed to work