This is what I have so far 

 

@SubscribeEvent
    public void onPreEntitySpawn(PotentialSpawns e)
    {
        if(e.getWorld().isRemote)
            return;

        List<SpawnListEntry> spawnListEntryList = e.getList();
        Iterator<SpawnListEntry> spawnListEntryIterator = spawnListEntryList.listIterator();

        while(spawnListEntryIterator.hasNext())
        {
            SpawnListEntry spawnListEntry = spawnListEntryIterator.next();

            if(spawnListEntry.entityClass.equals(EntityUndead.class))
            {
                Chunk chunk = e.getWorld().getChunkFromBlockCoords(e.getPos());
                int undeadCount = 0;

                ClassInheritanceMultiMap<Entity>[] entityInheirtanceMapList = chunk.getEntityLists();

                for(ClassInheritanceMultiMap<Entity> entityInheritanceMap : entityInheirtanceMapList)
                {
                    Iterable<EntityUndead> entityList = entityInheritanceMap.getByClass(EntityUndead.class);

                    for (EntityUndead ignored : entityList)
                        undeadCount++;
                }

                System.out.println(e.getPos().toString() + " Undead Count: " + undeadCount);
            }
        }
    }

 

The reason I need this is to control the number of my own custom entity on a chunk. So what I am trying to achieve here so removing PotentialSpawn of my custom creature on a chunk that has surpassed the max number of my custom entity per chunk. However, it doesn't look clean at all and is pretty inefficient. Any other ways to achieve the same thing?

I ended up doing this. Not sure if it's more efficient but it's less code to write.

 

@SubscribeEvent
    public void onLivingSpawnCheck(LivingSpawnEvent.CheckSpawn e)
    {
        if(e.getWorld().isRemote)
            return;

        if(!(e.getEntityLiving() instanceof EntityUndead))
            return;

        int range = 64;

        float minX = e.getX() - range;
        float minY = e.getY() - range;
        float minZ = e.getZ() - range;

        float maxX = e.getX() + range;
        float maxY = e.getY() + range;
        float maxZ = e.getZ() + range;

        List<EntityUndead> entityUndeadList = e.getWorld().getEntitiesWithinAABB(EntityUndead.class, new AxisAlignedBB(minX, minY, minZ, maxX, maxY, maxZ));

        if(entityUndeadList.size() > 5)
            e.setResult(Result.DENY);
    }