Boss Rules

Boss Rules

Boss rules allow you to transform regular mobs into powerful boss creatures with custom abilities, boss bars, minions, and more!

Location

data/botzmobleveling/mob_levels/bosses/<rulename>.json

Basic Structure

{
  "enabled": true,
  "target_mobs": ["minecraft:zombie"],
  "spawn_chance": 0.05,
  "structures": [],
  "biomes": [],
  "display_name": "Boss Zombie",
  "tier": 1,
  "level": 100,
  "ignore_level_cap": true,
  "boss_bar": {
    "color": "red",
    "style": "progress",
    "visible": true
  },
  "size_multiplier": 1.5,
  "glow_effect": true,
  "glow_color": "red",
  "particle_effect": "minecraft:flame",
  "immunities": [],
  "stat_multipliers": {},
  "xp_multiplier": 5.0,
  "loot_table": null,
  "minions": null
}

Field Reference

Core Fields

Field	Type	Default	Description
enabled	Boolean	true	Toggle this boss rule on/off
target_mobs	Array	[]	List of mob IDs that can become this boss. Empty = any mob
spawn_chance	Double	0.1	Chance (0.0-1.0) for an eligible mob to become this boss
structures	Array	[]	Restrict to specific structures. Empty = anywhere
biomes	Array	[]	Restrict to specific biomes. Empty = any biome

Boss Properties

Field	Type	Default	Description
display_name	String	"Boss"	Name shown above boss. Supports color codes
tier	Integer	1	Boss tier (1 = normal, 2 = elite, 3 = legendary)
level	Integer	50	The boss's level. Applied to the mob and used for its nameplate, boss bar, kill XP, and attribute scaling. Clamped to the global cap unless ignore_level_cap is true
ignore_level_cap	Boolean	true	Let level exceed the global level cap

Stats = level scaling + stat_multipliers. A boss's final stats come from two sources: (1) the spawn rule's attribute_scaling re-applied at the boss level, and (2) the flat stat_multipliers below, which multiply the mob's base value. Use level for "how high-level is it," and stat_multipliers for a guaranteed extra spike (e.g. max_health: 50.0 = 50× base HP).

Visual Effects

Field	Type	Default	Description
size_multiplier	Float	1.0	⚠️ Not functional in 1.20.1 — parsed and stored, but model resizing requires a rendering mixin that doesn't exist yet. Has no visual effect.
glow_effect	Boolean	true	Apply glowing effect
glow_color	String	"red"	Color of the glow
particle_effect	String	null	Particle ID emitted around the boss (simple particles like minecraft:flame, minecraft:soul).

Boss Bar

Field	Type	Default	Description
boss_bar.color	String	"red"	Boss bar color
boss_bar.style	String	"progress"	Boss bar style
boss_bar.visible	Boolean	true	Show the boss bar

Combat

Field	Type	Default	Description
immunities	Array	[]	Damage types the boss is immune to
stat_multipliers	Object	{}	Attribute multipliers
xp_multiplier	Double	5.0	XP drop multiplier
loot_table	String	null	Custom loot table ID

Minions

Field	Type	Default	Description
minions.type	String	Required	Mob type to spawn as minions
minions.count	Integer	2	Minions per spawn wave
minions.interval_seconds	Integer	30	Time between spawn waves
minions.health_threshold	Double	0.5	HP% to trigger spawning (0.0-1.0)
minions.max_minions	Integer	10	Maximum active minions

Color Codes

Display Name Colors

Use Minecraft color codes with §:

Code	Color
§0	Black
§1	Dark Blue
§2	Dark Green
§3	Dark Aqua
§4	Dark Red
§5	Dark Purple
§6	Gold
§7	Gray
§8	Dark Gray
§9	Blue
§a	Green
§b	Aqua
§c	Red
§d	Light Purple
§e	Yellow
§f	White
§l	Bold
§o	Italic
§n	Underline
§k	Obfuscated
§r	Reset

Example: "§4§l☠ Cluckthulhu §4§l☠" = Dark red, bold, with skull symbols

Boss Bar Colors

• red
• blue
• green
• yellow
• purple
• pink
• white

Boss Bar Styles

• progress - Solid bar
• notched_6 - 6 segments
• notched_10 - 10 segments
• notched_12 - 12 segments
• notched_20 - 20 segments

Immunity Types

Type	Blocks
fire	Fire, lava, fire aspect
fall	Fall damage
drown	Drowning damage
explosion	Explosion damage
projectile	Arrow, trident damage
magic	Potion damage
wither	Wither effect
cactus	Cactus damage
lightning	Lightning strikes

Complete Examples

Legendary Stronghold Chicken Boss

{
  "enabled": true,
  "target_mobs": ["minecraft:chicken"],
  "spawn_chance": 0.10,
  "structures": ["minecraft:stronghold"],

  "display_name": "§4§l☠ Cluckthulhu §4§l☠",
  "tier": 3,
  "level": 750,
  "ignore_level_cap": true,

  "boss_bar": {
    "color": "red",
    "style": "notched_10",
    "visible": true
  },

  "size_multiplier": 2.0,
  "glow_effect": true,
  "glow_color": "red",
  "particle_effect": "minecraft:flame",

  "immunities": ["fire", "fall"],

  "stat_multipliers": {
    "minecraft:generic.max_health": 50.0,
    "minecraft:generic.attack_damage": 10.0,
    "minecraft:generic.movement_speed": 1.5,
    "minecraft:generic.knockback_resistance": 0.8
  },

  "xp_multiplier": 20.0,

  "minions": {
    "type": "minecraft:chicken",
    "count": 3,
    "interval_seconds": 20,
    "health_threshold": 0.5,
    "max_minions": 9
  }
}

Nether Fortress Elite Guard

{
  "enabled": true,
  "target_mobs": ["minecraft:wither_skeleton"],
  "spawn_chance": 0.02,
  "structures": ["minecraft:fortress"],

  "display_name": "§5§lFortress Champion",
  "tier": 2,
  "level": 300,
  "ignore_level_cap": true,

  "boss_bar": {
    "color": "purple",
    "style": "notched_6",
    "visible": true
  },

  "size_multiplier": 1.3,
  "glow_effect": true,
  "glow_color": "purple",
  "particle_effect": "minecraft:soul",

  "immunities": ["fire", "wither"],

  "stat_multipliers": {
    "minecraft:generic.max_health": 15.0,
    "minecraft:generic.attack_damage": 3.0,
    "minecraft:generic.armor": 2.0
  },

  "xp_multiplier": 10.0
}

World Boss (Anywhere)

{
  "enabled": true,
  "target_mobs": ["minecraft:skeleton"],
  "spawn_chance": 0.001,

  "display_name": "§e§lSkeleton King",
  "tier": 3,
  "level": 500,
  "ignore_level_cap": true,

  "boss_bar": {
    "color": "yellow",
    "style": "notched_20",
    "visible": true
  },

  "size_multiplier": 2.5,
  "glow_effect": true,
  "glow_color": "yellow",
  "particle_effect": "minecraft:enchanted_hit",

  "immunities": ["fire", "projectile", "fall"],

  "stat_multipliers": {
    "minecraft:generic.max_health": 100.0,
    "minecraft:generic.attack_damage": 15.0,
    "minecraft:generic.movement_speed": 1.2,
    "minecraft:generic.knockback_resistance": 1.0
  },

  "xp_multiplier": 50.0,

  "minions": {
    "type": "minecraft:skeleton",
    "count": 5,
    "interval_seconds": 15,
    "health_threshold": 0.75,
    "max_minions": 15
  }
}

How Boss Spawning Works

1. A mob spawns normally
2. If it matches target_mobs (or list is empty)
3. AND it's in a valid structure (or list is empty)
4. AND it's in a valid biome (or list is empty)
5. THEN roll spawn_chance
6. If roll succeeds, mob becomes a boss

Tip: Use low spawn chances (0.01-0.05) for powerful bosses to keep them rare and exciting!

⚠️ Boss rules are for random spawns

Boss rules roll spawn_chance when a mob spawns naturally and turn it into a boss. They are not a way to give a specific named entity a guaranteed level. If you just want "this mob always spawns at level X," you usually want a mob override (fixed_level or level_bonus) instead, which scales the mob without the boss bar/minions/announcement machinery.

⚠️ structures won't match altar-/ritual-summoned bosses

The structures filter requires the mob to be standing inside a registered structure piece at spawn time. Mobs that are summoned by an item or ritual (e.g. Cataclysm's Ignis at a Blazing Eye altar, or boss-anchor spawns) are not placed by structure generation, so getStructureWithPieceAt finds nothing and the rule is skipped — even if the altar sits visually inside the structure.

For those bosses, leave structures empty (the boss can then spawn anywhere the target_mobs appear) and rely on spawn_chance/biomes to gate it. If you need a guaranteed level for a summoned mob, use a mob_overrides entry on a base/biome/dimension rule instead — see Mob Overrides → Scaling Specific Mobs Harder Than the Rest.

Config Integration

The boss module can be toggled in the config:

[bossModule]
enabled = true
showBossBar = true
bossBarRenderDistance = 64
preventDespawn = true
glowEffect = true
spawnAnnouncement = true
announcementRadius = 64

These global settings can be overridden per-boss in the datapack.

Tips

1. Start with low spawn chances - Bosses should feel special
2. Use tiered difficulties - Tier 1 for dungeons, Tier 3 for raids
3. Balance minion spawning - Too many minions can cause lag
4. Test in creative - Spawn mobs manually to test boss configuration
5. Combine with structure rules - Make entire dungeons challenging