Minecraft Custom Bosses: Mobs, Bars and Summons

Written for Minecraft 26.3.

Minecraft custom bosses start from a vanilla mob with stronger attributes, special gear and a name. You add a boss bar with /bossbar. Anything smarter, such as new attacks, is where a plugin like MythicMobs comes in.

Before you start

• Minecraft Java Edition 26.3, data pack format 121.0.

• Operator rights: /summon and /bossbar need permission level 2.

• A command block, a function or a plugin if you want to spawn bosses repeatedly.

Summon the mob

Vanilla stores the mob's stats as entity data. Put them in the summon command as SNBT:

/summon zombie ~ ~ ~ {CustomName:'{"text":"Mine King","color":"red"}',CustomNameVisible:1b,PersistenceRequired:1b,Health:200.0f,attributes:[{id:"minecraft:max_health",base:200.0d}],equipment:{mainhand:{id:"minecraft:iron_sword",count:1}},drop_chances:{mainhand:0.0f},Tags:["boss"]}

• attributes set base values such as minecraft:max_health. Set Health to match, or the mob starts at the default.

• equipment holds slots: head, chest, legs, feet, mainhand, offhand, body and saddle.

• drop_chances defaults to 0.085 per slot. Set 0 to stop gear dropping.

• PersistenceRequired stops it despawning. Tags lets commands select it.

• active_effects takes entries with id, amplifier and duration. A duration of -1 is infinite.

Use a loot table for its drops. See loot tables.

Add a boss bar

1. Create the bar: /bossbar add example:king "Mine King"

2. Style it: /bossbar set example:king color red and /bossbar set example:king style notched_10

3. Set the range: /bossbar set example:king max 200 and /bossbar set example:king value 200

4. Show it: /bossbar set example:king players @a

Colours are blue, green, pink, purple, red, white and yellow. Styles are progress, notched_6, notched_10, notched_12 and notched_20. Remove it with /bossbar remove example:king.

The bar does not follow health. Vanilla only draws bars for the Wither, the Ender Dragon and raids. Your bar is a separate object: update its value with a function or a plugin.

Make it look custom

A mob's model cannot be swapped by a pack alone. The usual approach is to hide the mob and attach display entities with a Blockbench model. See custom blocks for how display entities work. That needs a plugin to move and animate them.

Data-driven mob variants exist for some mobs, but this guide did not verify the format, so it does not cover them.

When to use a plugin

MythicMobs and similar plugins give you skills, phases, spawners and health-linked bars from config files. Use vanilla for a one-off event, a plugin for anything you will run every week. See also optimizations for keeping entity counts low.

Check it worked

• The mob spawns with its name above it.

• Check its health with the debug screen or hit it: it should take many hits.

• The bar shows for the players you chose.

Common problems

The boss despawns

Add PersistenceRequired:1b.

The health bar is wrong

Set both the attribute and Health. The bar max must match too.

The summon fails

Check the quotes. SNBT strings with JSON inside need single quotes outside.

The bar shows for nobody

The default for players is none. Set it.