Universal Boss Respawner

A standalone, data-driven revival system for bosses and mobs from other mods.

This mod extracts Cataclysm's Boss Respawner into an independent system that can revive bosses and mobs from other mods — and it is fully data-driven.

Have you ever found a boss structure on a server, only to discover that the boss has already been defeated, leaving you to search for another one? This mod solves that problem.

Designed for modpack authors and server owners: create a data pack following the documented format, and a configured boss will generate a Boss Respawner cage when defeated. Use the configured revival item to summon the boss again, turning formerly one-time bosses into repeatable encounters.

Built-in Mod Support

The mod ships with 30 rules. Boss names and revival items are listed below; the matching item IDs are in the built-in JSON files.

Twilight Forest

The eight progression bosses use Twilight Forest's own HomePos anchor. The cage is placed beside the boss's reward chest after the chest has spawned; the Lich replaces its chest with its spawner, so collect the loot first.

Legendary Monsters

The Obliterator is a summoned boss and does not need a respawn cage.

Mowzie's Mobs

Bosses Rise

Bosses Rise's Yeti and Kraken are not supported: their custom death and ship-anchor logic cannot be reproduced reliably by a static cage.

Jade Integration

Jade is optional. When it is installed, looking at a respawn cage shows:

• the boss it will revive;
• the required key item, with the amount when more than one is needed.

The information works on multiplayer servers and needs no extra configuration.

Data-Driven: Add Any Boss

Every rule is a JSON file. You can support a boss from another mod without writing Java code.

1. Create a data pack

Create a normal data pack with a pack.mcmeta file:

{
  "pack": {
    "pack_format": 48,
    "description": "My Boss Respawner rules"
  }
}

pack_format 48 is for Minecraft 1.21.1.

2. Add a rule

Place the rule at:

data/my_pack/boss_respawner/entries/my_boss.json

A minimal rule looks like this:

{
  "schema_version": 4,
  "entity": "modid:boss",
  "activation": {
    "item": "modid:key"
  },
  "placement": {
    "mode": "home",
    "home": {}
  },
  "spawn": {
    "mode": "summon",
    "summon": {}
  }
}

Replace modid:boss and modid:key with the IDs from the boss mod. home returns the boss to where it was first observed; use "mode": "death" with a death object if the boss has no fixed arena. Omit optional fields to use defaults.

3. Reload and test

Put the data pack in the world's datapacks folder and run /reload. Add the rule before the boss is first seen; reloading also registers currently loaded bosses. Use the built-in JSON files as complete templates.

Installation

• Minecraft: 1.21.1
• Loader: NeoForge 21.1.219 or newer
• Java: 21
• Install on both the client and the server.
• Cataclysm, Twilight Forest, Legendary Monsters, Mowzie's Mobs, Bosses Rise, and Jade are all optional.
• The respawn cage is an admin/creative block: it is not craftable or breakable in survival. Use /give or the creative spawn-egg tab when setting up an arena.

Configuration

The common config includes:

• a master switch for new placement and spawning;
• a glowing outline for cages, with adjustable range;
• debug logging.

Per-rule settings live in the JSON: placement mode, search ranges, key item, spawn count, duplicate handling, and more. The defaults work out of the box.

Good to Know

• Cataclysm is not required; it is only the inspiration for the original respawner concept.
• Bosses Rise's Yeti and Kraken are intentionally unsupported and have no built-in rules.
• The Lich's reward chest is replaced by its spawner; loot it before activating the cage.
• Cages cannot be broken in survival. Test custom placements before putting them on a live server.
• Rules for mods that are not installed are skipped safely.

Credits

Inspired by Cataclysm's boss respawner. Thanks to the authors of Cataclysm.