Install L_Ender's Cataclysm on your server

L_Ender's Cataclysm adds difficult dungeons, hard boss fights and powerful gear. It runs on Forge and NeoForge only, with no Fabric version, and every player needs the same file on their own game.

Checked against L_Ender's Cataclysm 3.33 on NeoForge 1.21.1, October 2026.

What you need

• NeoForge on Minecraft 1.21.1. Cataclysm 3.33 asks for NeoForge 21.1.0 or newer. Pick 1.21.1 in JAR Manager and the panel runs it on Java 21 for you.
• Curios API and Lionfish API. Both are required, and Modrinth lists both as dependencies of this file, so the install window offers them. The jar asks for Curios 9.2.2 or newer, and for Lionfish API 3.1.
• Forge 1.20.1 instead? Cataclysm 3.31 covers Forge 1.20.1. Modrinth lists Lionfish API and Curios as required there as well, and the jar asks for Lionfish API 3.0 or newer and Forge 47 or newer.
• A large file. The jar is about 73 MB, so it takes a minute or so to appear in the mods folder after you install it.

Switch the server to NeoForge 1.21.1

1. Open JAR Manager, under More in the left rail.
2. Set Server software to NeoForge and Minecraft version to 1.21.1, then press Apply change.
3. Leave Take a backup first ticked, press and hold Confirm & reinstall, and wait for the console to finish.

The screen warns that configuration files may be reset. Change your Minecraft version or mod loader covers the switch in full.

Install it

1. Open the Mods tab under Content and leave the Modrinth source chip selected.
2. Search for Cataclysm and press Install on L_Ender's Cataclysm. A window titled "Needs 2 more add-ons" lists Curios API and Lionfish-API. Press Install all (3). The jar is saved as L_Enders Cataclysm 1.21.1-3.33.jar, without the apostrophe.
3. Go to Console, press Start and accept the EULA prompt the first time. The server is ready when the console shows Done.

Find the dungeons

The jar defines these structures, among others: cataclysm:sunken_city, cataclysm:soul_black_smith, cataclysm:ancient_factory, cataclysm:burning_arena, cataclysm:frosted_prison, cataclysm:ruined_citadel, cataclysm:cursed_pyramid and cataclysm:acropolis. As an operator, run /locate structure cataclysm:sunken_city in game, and the game reports coordinates. Swap in any of the other names.

The bosses in this version include the Netherite Monstrosity, Ignis, the Ender Guardian, The Harbinger and The Leviathan. The project describes the fights as challenging.

Tune the bosses

After the first start, open cataclysm-common.toml in the config folder with the File Manager. Each boss has its own tables under [mobs.<boss>], such as [mobs.ender_guardian]. Its [mobs.<boss>.combat_config] table holds health_multiplier and attack_multiplier (the Ender Guardian's health_multiplier is 1.0 by default), and its [mobs.<boss>.cap_config] table holds damage_cap. Raise or lower a multiplier, press Save and restart the server, because NeoForge reads this kind of config as the game sets up.

If the server struggles during fights, read Why is my server lagging? and How much RAM does my Minecraft server need?.

Common problems

• The server stops at start and names curios or lionfishapi. Install the missing library from the Mods tab, in the build for NeoForge 1.21.1.
• It says Lionfish API is the wrong version. Cataclysm 3.33 names version 3.1. Install that one, then press Check for updates in the Installed view.
• Players cannot join. They need NeoForge 1.21.1 and the same Cataclysm, Curios and Lionfish files. Use Export for players in the Installed view of the Mods tab for a zip of what they need, then read Join a modded server from your launcher.
• Other load errors. Fix Minecraft mod and plugin load errors shows how to read the log.