Add new mobs to your server with mods

A mob mod adds new animals and monsters to the world, each with its own behaviour and drops. Alex's Mobs is the worked example here, because its Modrinth page describes 89 new mobs, from grizzly bears and orcas to bone serpents. The same steps work for any other mob mod.

Checked against Alex's Mobs 1.22.9 and Citadel 2.6.3 on Forge, Minecraft 1.20.1, October 2026.

What it needs

Mobs can only be added by a mod, so the server has to run a mod loader. Paper and Purpur load plugins, not mods (Minecraft plugins vs mods).

• Loader and version: Alex's Mobs 1.22.9, the newest official release on Modrinth, is built for Minecraft 1.20.1 on Forge. Run Forge on Minecraft 1.20.1.
• Citadel: a library mod from the same author that Alex's Mobs requires. The store installs it for you.
• Players: Modrinth marks Alex's Mobs as required on both the client and the server. Every player needs the mod and Citadel on their own computer, and Forge on Minecraft 1.20.1 to run them.

Switch the server to Forge 1.20.1

1. Make a backup in the Backups tab.
2. Open JAR Manager, under More in the panel menu.
3. Pick Forge under Server software and 1.20.1 under Minecraft version, then click Apply change.
4. In the Reinstall server? box, leave Take a backup first ticked, then press and hold the Hold to Confirm & reinstall button until its bar fills, about three seconds. A plain click does nothing. If the box lists add-ons that have no build for Forge, it also offers to disable them (kept, not deleted); leave that ticked, because unticking it changes the button to Hold to Switch anyway. Your world is kept, and some configuration files can reset.

A world that has been upgraded to Minecraft 26.1 or newer can't be loaded in an older version: Paper's 26.1 announcement and Mojang's 26.1 snapshot notes both say so. If your world has been on 26.1 or newer, it can't go back to 1.20.1, so start fresh or use a world made on 1.20.1 or older.

Install the mod

1. Open the Mods tab and keep the Modrinth chip selected.
2. Search for Alex's Mobs. Choose the one by AlexModGuy. Others, such as unofficial ports and compatibility add-ons, are separate projects.
3. Click Install. A box titled Needs 1 more add-on lists Citadel. Click Install all (2).
4. Restart from the Console tab.

Get your players ready

In the Installed view, click Export for players. A box opens with a Download zip button. The zip packs the mods your players need with instructions and leaves out server-only mods. Send them that, and tell them to use Forge for Minecraft 1.20.1 too.

When someone joins a world with Alex's Mobs for the first time, they're given an Animal Dictionary book that describes each creature. If it's lost, it's crafted from a vanilla book, a green dye and one of the mod's mob drops, such as bear fur or a crocodile scute.

Change how mobs spawn

After the first start, the mod creates alexsmobs.toml in your config folder. Stop the server and edit it in the File Manager. Each mob has a spawn weight, such as grizzlyBearSpawnWeight, from 0 to 1000. Higher numbers make it spawn more often among a biome's mobs, and 0 turns that mob's spawning off. The giveBookOnStartup setting, true by default, controls the Animal Dictionary.

If a mob mod makes the world too crowded or the server lags, lowering the spawn weights is the first thing to try (Why is my server lagging?).

Find other mob mods

In the Mods tab, open Add filter, choose Category and pick Mobs. Leave Game version and Loader on your server's values. A row marked Client only can't go on a server, because it only runs on a player's own game.

If something goes wrong

• The server stops during start-up: open the Installed view and look for a Needs or Failed to load badge. Install the missing mod, or remove the one that fails.
• A player can't join: check they have the same mods and Minecraft version as the server. Send them a fresh Export for players zip.
• Plugins you used before stopped working: Forge doesn't load Paper plugins. Minecraft plugins vs mods lists what to use instead.