Category: Minecraft

Minecraft Monster Spawners

Noah Petherbridge
kirsle
Posted by Noah Petherbridge on Saturday, January 25 2014 @ 05:25:54 AM
Update for Minecraft 1.9: the syntax for the mob spawner commands have been changed starting in Minecraft 1.9

You can read the rest of this blog post for all the examples, but the main key difference is that the EntityId tag has been removed and you need to do SpawnData:{id: EntityIdHere} instead, replacing "EntityIdHere" with the entity ID you want (Zombie, Skeleton, PigZombie, VillagerGolem, etc.)

So, for the /setblock command:

Old way: /setblock ~ ~ ~ mob_spawner 0 replace {EntityId:Zombie}
New way: /setblock ~ ~ ~ mob_spawner 0 replace {SpawnData:{id:Zombie}}

And for the /give command:

Old way: /give @p mob_spawner 1 0 {BlockEntityTag:{EntityId:Skeleton}, display:{Name:Skeleton Spawner}}
New way: /give @p mob_spawner 1 0 {BlockEntityTag:{SpawnData:{id:Skeleton}}, display:{Name:Skeleton Spawner}}

So when you see examples below, translate them into the new format for Minecraft 1.9. I may eventually write a new version of this blog post that contains only 1.9 commands, but for now you'll have to rewrite them manually.

Edit 2: there seems to be a bug in 1.9 where a spawner given with the /give command will only spawn its monster one time before reverting to a pig spawner. The SpawnPotentials seems to be the culprit; when the block is placed it gets initialized to a list that only includes pigs. The list is supposed to be empty by default, so explicitly setting it to empty seems to work:

/give @p mob_spawner 1 0 {BlockEntityTag:{SpawnData:{id:Skeleton},SpawnPotentials:[]}}

The original blog post follows.

--Updated on 3/17/2016


Minecraft 1.7 added the commands /summon, /setblock, and an extended syntax for /give, so that you could summon any entity, and attach a ton of NBT Tags on it to control attributes like what equipment it's wearing or whether it's invulnerable. ;)

I was excited about this because not only could I spawn an Enderdragon in the overworld (this never ends well), but it would open up the possibility to just give myself custom monster spawners, like those typically found in a zombie/skeleton/spider dungeon.

Unfortunately, the /give command doesn't seem to allow you to add a monster spawner to your inventory. At most, you'll get a Pig Spawner, which has always been the default monster if you would /give yourself a spawner in the past. But, if you use /setblock you can just set a block to be a monster spawner and do it that way. Update: since writing this I found the syntax for giving a mob spawner with /give. Example:

/give @p mob_spawner 1 0 {BlockEntityTag:{EntityId:Skeleton}, display:{Name:Skeleton Spawner}}
This gives a Skeleton Spawner in your inventory. The display: stuff is just to give it a custom name, otherwise it will call itself "Mob Spawner" in your inventory. If you're gonna carry multiple spawners, the names will help differentiate them. Everything inside the BlockEntityTag part are the same tags from the /setblock examples below.

Now back to the original post...

The Usual Monsters

Pictured above are your "naturally occurring" monster spawners along the bottom: Blaze (in Nether Fortresses), Skeleton, Zombie, Spider, and Cave Spider (in abandoned mineshafts). I've also created spawners along the top for: Magma Cube, Slime, Zombie Pigman, Creeper, and Enderman.

The basic command syntax is along these lines:

/setblock ~ ~ ~ mob_spawner 0 destroy {EntityId:Zombie}
Replace the value for EntityId for any other valid entity. There's a list of Entity IDs on the Minecraft Wiki. You can create a monster spawner for pretty much every monster in the game, including the bosses like the Enderdragon and Wither.

The Bosses

/setblock ~ ~ ~ mob_spawner 0 destroy {EntityId:EnderDragon}
/setblock ~ ~ ~ mob_spawner 0 destroy {EntityId:WitherBoss}
Things to watch out for: the Enderdragon will destroy every block it touches except for Bedrock, Obsidian, and End Stone (a.k.a. the only three types of blocks that naturally occur in the End Dimension), so it will destroy its own spawner, and if you create one in the overworld or the Nether, it will ruin everything it touches. You can mitigate this by turning off monster griefing with the command /gamerule mobGriefing false.

Giants!

With this command you can also create a spawner for the Giant. This monster has been in the game for ages but never officially used. It's a super-huge zombie. However, I couldn't get this spawner to actually create a Giant for me. :( Your mileage may vary. You'll probably be better off summoning it directly with /summon Giant.

/setblock ~ ~ ~ mob_spawner 0 destroy {EntityId:Giant}
Horses!

You can also create a mob spawner for horses! (edit/warning: this worked for me when I originally wrote this post, but others have reported that horse spawners tend to crash their games. I can reproduce this behavior now too in Minecraft 1.7.10 and a few others I tried (1.7.9, 1.7.2). There's a Minecraft bug ticket for this. YMMV. It seems to work in snapshot 14w31a (screenshot) so may be fixed for 1.8)

The zombie and skeletal horses aren't naturally occurring in-game, and they cannot be tamed normally like other horses. You'll want to make sure the "Tame" flag is set when spawning these so that players can ride them. They can equip saddles, but not armor.

Zombie: /setblock ~ ~ ~ mob_spawner 0 destroy {EntityId:EntityHorse,SpawnData:{Type:3,Tame:1}}
Skeletal: /setblock ~ ~ ~ mob_spawner 0 destroy {EntityId:EntityHorse,SpawnData:{Type:4,Tame:1}}
Again, warning: horse spawners with SpawnData may crash your game. It's a known bug in several versions of Minecraft. If this happens, and your game managed to save the world before the crash, so that it instantly crashes again when rejoining the game, you'll have to use a third-party tool like MCEdit to delete the offending spawner.

That "SpawnData" attribute from the previous command is how you can attach NBT data to the spawned entity. Horses take a Type attribute and Tame, among some others. You can see all the relevant NBT tags at "Chunk format" on the Minecraft Wiki.

Here's a more advanced command that creates a Zombie spawner where the zombies are all equipped with Diamond Swords. I found this one from the Minecraft forums (I don't know or care too much about the NBT format; I usually just create simple spawners as listed above in this post).

/setblock ~ ~1 ~ minecraft:mob_spawner 0 replace {EntityId:Zombie,SpawnData:{Equipment:[{id:276,Count:1}]},SpawnPotentials:[{Type:Zombie,Weight:1,Properties:{Equipment:[{},{},{},{},{id:46,Count:1}]}}],SpawnCount:2}
Note: You'll have to paste that into a Command Block (/give <your_name> command_block) because the command is too long for the chat console. Attach a button to the command block with Shift+RightClick, push it and the spawner will appear above the block.

Custom Zombies

Vanilla Minecraft Tricks

Noah Petherbridge
kirsle
Posted by Noah Petherbridge on Wednesday, November 20 2013 @ 11:34:59 AM
I run a couple of Minecraft servers, and I always prefer to run the default vanilla server as provided by Mojang - mainly because the custom servers like Bukkit always lag behind by weeks or sometimes months every time a new version of Minecraft is released, and partly because there's just way too many custom plugins for Bukkit, many of which do the same things in different ways while being incompatible with each other and it's a huge mess.

I liked the idea of some of Bukkit's plugins, though, so I'm always trying to find creative ways to get similar results using just the vanilla server. Here's a few tricks I figured out myself or heard about from Reddit.

Spawn Region Mechanics

Most of these tricks involve command blocks and understanding a few quirks about how Minecraft vanilla servers work.

Upon creating a new world, give yourself a compass and follow it to find the center of the world spawn region. I usually put a block here to visually remind myself where the center is, because the spawn region is important for a couple of reasons.

Firstly, the spawn region is always kept loaded in memory, along with the 5x5 chunk radius surrounding the spawn point (where a chunk is a 16x16 block section of the world). This is important because it means that if you set up any Redstone devices that run on a loop, they'll run all the time even if all the players wander far away from the spawn area. So it's a good place to incorporate command block circuits to enforce global "rules" on your server.

The other important thing is the spawn protection radius, which is the number of blocks around the spawn point (where the compass points) in which non-operator players are not allowed to place or destroy blocks, or interact with most items. By default the radius is set to 16 blocks, and is configurable in the server.properties file.

In the spawn protection radius, non-op players can't place or destroy blocks, and they can't use any devices except for pressure plates and trip wires. They can't even open or close wooden doors, they can't use crafting tables or furnaces, etc. Only the server operators have rights in the protection radius.

However, the protected area is not safe from monsters or outside interference, so for example if a player lures a Creeper into the spawn region it can still blow up blocks (unless you turn off mob griefing with /gamerule mobGriefing off, which prevents Creepers and other mobs from changing blocks). Clever players can also fling TNT in from outside the protected region to destroy blocks inside. When in doubt, encase your Redstone circuits in bedrock bunkers and keep them hidden away from view. ;)

Command Blocks

Clever use of command blocks can enforce "rules" on a server, for example if you want to ban the use of TNT, you can have a command block be executed very rapidly that removes TNT from all player inventories, by running the command /clear @a minecraft:tnt.

All your command block redstone circuits should use a clock circuit of some kind (one that will run in an infinite loop). Ideally, the circuit should be self-starting, especially if the circuit is NOT within the 5x5 chunk spawn radius. This is because when the chunks that contain a redstone circuit are unloaded, the circuit stops running, and when the chunks are reloaded (because a player walks closer to them), you want your circuit to automatically start back up.

See clock circuits for some ideas. An example I use is where you have a redstone torch that powers a circuit, and the circuit eventually extends a piston over an earlier part of the circuit to interrupt its own power. With the power interrupted, the piston retracts, allowing the circuit to be powered again by the redstone torch, and so on.

Griefer Protection

The easy way to prevent players from breaking your structures is to build everything important within the protected spawn radius. If you also turn off mob griefing, and use a command block to remove TNT from player inventories, it's highly unlikely they'll find a way to break things in the spawn region.

Outside the spawn region, a useful tip I saw on Reddit is to apply the Mining Fatigue V effect to all players within a certain radius of your building. For example, create a redstone clock near the middle of your building that runs a command block to run this command:

/effect @a[r=60,m=0] 4 3 5
This will apply an affect to all players (@a), who are within 60 blocks of the command block and who are in Survival Mode (m=0), the Mining Fatigue effect (ID 4), for 3 seconds, at level 5. Mining Fatigue level 5 basically makes it 100% impossible for the player to mine a block, even if they have a diamond pickaxe, even if it's enchanted. The player can't even break a flower under this condition.

The 3 second interval would be adjusted depending on how frequently your clock runs the command. You want it to only affect players while they're within the general area of your building, and lift the effect quickly if they leave.

Controlling the Spawn Location

In certain maps, you might like to have much finer-grained control over where exactly users on your server will spawn. In vanilla Minecraft, users will spawn somewhere within a 20x20 radius area centered around where the compass points. See Spawn/Multiplayer Details.

On one of my servers, I wanted all players to appear in the center of a room when they joined the server (or died without a bed) so that I could somewhat randomly disperse them around the world by having them pick a pressure plate that would teleport them somewhere. See my blog post "Fun with Command Blocks".

Basically, if you go this route, the actual world spawn point will not be used. Instead you'll just have a command block running on a clock that teleports anyone who appears in the spawn region to a destination somewhere else (you should make sure you teleport them far away from the spawn region, so that they'll be outside the radius of the command block that teleported them... otherwise you get caught in an infinite loop of teleportation!)

Example command for this command block to run:

/tp @a[m=0,r=25] X Y Z
Substitute X, Y and Z for the coordinates to teleport to. This command would snipe all users within a 25 block radius of the command block and teleport them off to those coordinates. Also make sure to include the "m=0" -- this will make it only teleport Survival Mode players away. This way, you (the operator) can switch your mode to Creative and be able to get close enough to the command block to edit it or whatever you need to do. But it will keep all the other players away by teleporting them to your designated "spawn location".

Adventure Mode

Adventure Mode might be considered for certain circumstances as a method of anti-grief protection. On one of my servers, I built a huge Parkour course in the End Dimension, and I hadn't heard about using Mining Fatigue V to prevent players from griefing the parkour course, and things in The End aren't protected by the world spawn region, obviously.

What I did was encased the End Dimension Spawn Platform in bedrock, with the only exits to either go back through the Exit Portal, or step on a pressure plate that would teleport them into the Parkour course (if somebody destroys the pressure plate, then nobody can get into the parkour course, but it's better than allowing them to vandalize the course itself).

The pressure plate would run a few command blocks - one would clear all their inventory with /clear, another one would change their game mode to Adventure with /gamemode 2 @p, and the last one would finally teleport them into the course.

A command block clock in the overworld would set all adventure mode players back to survival in case they died and respawned, with /gamemode 0 @a[m=2].

The thing to know about Adventure Mode, though, is that it's basically "Strict" Survival Mode. If a block requires a specific class of tool to break it (stone needs a pickaxe, wood needs an axe), then only that tool is allowed to be used. If you swing an axe at stone, or a pickaxe at dirt, then your player just swings once as if hitting air, and then nothing.

You don't necessarily need to use the right material of tool, just the right tool. For example Adventure Mode allows you to destroy obsidian using a wooden pickaxe, even though the wooden pickaxe won't drop the obsidian block. So for Adventure Mode to work, you basically need to remove ALL tools from their inventory.

Even without tools, blocks that can be broken by hand are still vulnerable. So avoid using glass, torches, flowers, redstone devices (including buttons) which are in reach of the player, etc., as they can break these without needing any tools at all.

Update (8/14/15): As of Minecraft 1.8, the Adventure Mode behavior has been changed. Briefly:

  • Players in Adventure Mode can't break or place **any** blocks by default, even if they have the correct tool (e.g. with a pickaxe, they can **not** mine stone blocks by default).
  • The exception is that items have new `CanDestroy` and `CanPlaceOn` tags, so for example you could `/give` an Adventure Mode player a pickaxe with a `CanDestroy:["stone"]` tag, and that pickaxe can *only* destroy stone blocks but nothing else that isn't explicitly listed in the `CanDestroy` tag.
So, Adventure Mode as a way to grief-protect an area is even better in Minecraft 1.8 because it stops them from being able to break anything at all, and you don't have to /clear their inventory either!

Helpful Links

Scripting in Minecraft 1.7

Noah Petherbridge
kirsle
Posted by Noah Petherbridge on Monday, September 23 2013 @ 11:23:56 AM

One of the big features of the Raspberry Pi edition of Minecraft was that they provided a scripting API, so that you could write Python code to manipulate the blocks in the MineCraft world.

The scripting API hasn't officially come to the desktop version of Minecraft, but version 1.7 includes a handful of fun new server commands, like /setblock, /summon, and an extended interface for /give, so you can now summon any type of entity you want, including Ender Dragons, or summoning a Wither Skeleton riding on top of a Skeleton Horse while wearing fully enchanted diamond armor and holding a diamond sword.

But this post is going to focus on the /setblock command, which lets you change a block somewhere in your map by giving the coordinates to it and setting what type of block you want to put there.

When you're running a Minecraft server, you can enter server commands either in-game (if you're the operator), or directly into the terminal that's running the server. Using the latter, you can have a third party program (a Python script for example) write stuff into the terminal running the server, to automatically run server commands!

I made a quick proof-of-concept Python script to demonstrate this. This script will create a cube of stone of any dimensions you want somewhere in your Minecraft 1.7 server.

#!/usr/bin/python

# makecube.py - Proof of concept for scripting Minecraft 1.7
#
# Usage: makecube.py <screen_name> <size> <x> <y> <z>
#
# Works for Unix-like OS's only and depends on the `screen` command.
# Setup:
# [bash]$ screen -S minecraft
# [screen]$ java -jar minecraft_server.jar
# (in another terminal)
# [bash]$ makecube.py minecraft 25 0 60 0

from sys import argv
import os

material = "stone"
if len(argv) != 6:
    print "Usage: makecube.py <screen_name> <size> <x> <y> <z>"
    quit()

screen = argv[1]
size, x, y, z = map(lambda arg: int(arg), argv[2:])

def setblock(x, y, z):
    cmd = "screen -x {0} -X stuff '/setblock {1} {2} {3} stone 0 replace\x0D'"\
          .format(screen, x, y, z)
    os.system(cmd)

# Generate the cube's coords.
coords = list()
x1 = int(x - size/2)
y1 = int(y - size/2)
z1 = int(z - size/2)
for x2 in range(x1, x1 + size):
    for y2 in range(y1, y1 + size):
        for z2 in range(z1, z1 + size+1):
            coords.append([ x2, y2, z2 ])

# Send all the /setblock commands.
for coord in coords:
    setblock(*coord)

WorldPainter: Myst Island

Noah Petherbridge
kirsle
Posted by Noah Petherbridge on Thursday, June 13 2013 @ 12:56:39 PM
Recently, I've been playing around with WorldPainter. It's a tool for creating custom maps for Minecraft, where you can just paint on your mountains, valleys, lakes, biomes, trees, and other details about your map, and then export it as a new Minecraft map to play on.

It also has a feature to import a heightmap file, which is a grayscale image where brighter shades of white represent higher mountains, and lower shades are the lower elevations of the map. With this, you could design a terrain in a variety of different tools, export a heightmap of your terrain, and through WorldPainter, convert it into a Minecraft map. You can paint in the biomes and other features first in WorldPainter, of course.

I decided to test this using a heightmap I found of Myst Island (I found it on this Myst Online forum thread). Here's the original heightmap:

Myst

The image is 500x500 pixels, and the brightest shade of white is about 253, so if we imported this into WorldPainter as-is, half the island would be flooded (with the default water level of 62), and that mountain would reach higher than the clouds. So, first, I adjusted the levels in GIMP (Photoshop or something could've been used instead) to raise the lowest shade of black to just below the water level and lower the brightest shade to something more reasonable.

GIMP

Because the heightmap included some underwater hilly structures, I brought the lowest level up to 52 instead of 0, and lowered the highest level down to 120 from ~255. This resulted in the following image:

Myst w/ levels adjusted

After importing it into WorldPainter (via File->Import->Height map), this is how the map looked:

Myst in WorldPainter

I exported the map immediately to see how it would look in-game. I found that the original scale of the heightmap made the island a little bit too large, so I tried again but scaled it down to 50% when importing the heightmap. Here you can see the difference (click for larger versions):

Large Island
Myst Island

It's all a trial-and-error kind of thing. I had to tweak the levels of the heightmap a handful of times to get it to look just right, and scaling it down to 50% might not even be the perfect scale either (but you wouldn't know until you started trying to build on it). This is a pretty neat tool anyway. I'd probably recommend making your own terrains rather than trying to use someone else's (for example Myst Island), because then you'll get a lot fewer headaches when trying to build on the map and trying to get the scale just right and everything.

New Server

Noah Petherbridge
kirsle
Posted by Noah Petherbridge on Friday, May 31 2013 @ 04:12:30 AM
I've migrated Kirsle.net and all my other websites and MineCraft servers to a new home. They're now on a beefier dedicated server (8GB RAM instead of the old 4GB) which is actually 50% less expensive than the old server.

My Minecraft servers are being rearranged as well. This new machine has 5 IPv4 addresses, and each of my MC servers will get its own IP and hostname instead of having to juggle port numbers.

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