The NPC Respawner is a non-living entity that is invisible to players in survival mode. It functions as a continual spawner for two certain types of NPC, making sure that a naturally-generated structure isn't permanently stripped of its occupants.
Creative mode players may interact with the spawner, changing its properties or destroying it. They can also place new spawners using the item of the creative inventory.
The NPC Respawner can be found in many naturally-generated structures which contain NPCs. They are also present in player-placed structures made with the structure spawners.
The NPC Respawner can be found in the creative inventory or by using the commands:
/give @p lotr:item.npcRespawner /lotr_summon lotr.NPCRespawner
The usage seems to be kind of the same as a mob spawner, except you are able to fill in two different mobs, and set a home area of the non playable characters you require. This is very useful in creative mode for stocking structures with NPCs without having to worry about them wandering off, or having to continually respawn new ones.
But to actually use the NPC Respawner, all you have to do is right click in creative mode and you'll be greeted with an image like the one on the left. The first thing you'll probably look at is the two black boxes under "Primary Spawn Class" and "Secondary Spawn Class" These boxes will be the creatures spawning. To find a specific creature to use all you have to do is find the Spawn Egg containing the desired NPC and type the name you see when your mouse hovers over it, into the box for example: "lotr.Hobbit" Now let's look at the "Spawn Cap: " box, this box will determine how many NPCs will spawn.
The "Spawn Interval: " Boxes will determine the time before each spawn. In the image the time is set to 3:00 minutes this could also be set to seconds using the box on the right.
The "Block Enemy Spawns: " Box is used to deny the enemy of the NPC you placed in the spawner from naturally spawning. For example, if I placed a Gondor soldier in the spawner and set the Block Enemy Spawns to 64 blocks (The max) No orc will naturally spawn within those 64 blocks. Or you could just disable this option by bringing the bar to the "OFF" side as it is by default. Note that this can also block spawns in other NPC Respawners.
The "Spawn Mounts " Box is pretty self explanatory but it allows or denies The NPCs to spawn with mounts whether it's horses for Men, Ponies for Hobbits, Wargs for Orcs etc. It can also be set to default in which case the NPC will have the same chance of spawning with a mount as it does naturally
The "Home Distance: " Box will set the home of the spawning NPC's. Meaning they will either stay in that area or always return to it after fighting enemies.
Now for the more less important settings:
The "Check X/Z Range" The "Check Y Min: " AND The "Check Y Max: " Will make the NPC Spawner check that area before spawning the placed NPC. This option will prevent any over flowing of NPCs that prevents lag or potential crashes
The "Spawn X/Y Range: " The Spawn Y Min: " AND The "Spawn Y Max: " Means you can set the area the NPCs can or will spawn if disabled the NPCs will just spawn around the spawner.
And last the "Destroy" Button will completely remove the flag and all of its settings.
To get rid of a NPC respawner, you have to open its GUI in creative mode, and press the
"Destroy" button. It is not possible to remove it by left-clicking on it.
In previous versions of the LOTR mod (from Public Beta 6 up until the release of Public Beta 28), a similar system existed in the mod. Several structures such as the Gondor Fortress had NPC-respawning capability; however, these respawn locations were stored as coordinates in the save files, and thus were not easily accessible to players who might wish to change or remove a spawning location, or add new ones. Nor were new respawn locations created with player-placed structures. In addition, this meant that the game had to cycle through all saved coordinates and check if each was loaded in the world. On larger servers with much explored terrain, these lists of respawn coordinates could number in the thousands (or even higher) and cycling through all of these contributed significantly to server lag (which would worsen over time).
The NPC Respawner is a replacement for this older system, solving all of its drawbacks, with the aim of allowing players to alter or remove these respawning locations or add new ones. Since entities are only loaded into the game when their containing chunk is nearby, the server need not consider all respawn locations at once, and thus lag is greatly lessened.