Cobblemon Ultra-Beasts

Cobblemon Ultra-Beasts

Rare wormholes tear open in the overworld. Step through one and you land in Ultra-Space, a void dimension where a single Ultra Beast waits inside a structure built for it. Catch it, or leave empty-handed — either way the wormhole is gone when you get back.

Runs on Fabric and NeoForge, Minecraft 1.21.1, Cobblemon 1.8.4.

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How it works

A wormhole can appear near any player in the overworld, on a timer and a dice roll you control. It announces itself with a warden's sonic boom, drops out of the sky pulling debris into a collapsing swirl, and settles as a portal you can walk into. It lasts one minute, then closes.

Walk in and you're taken to Ultra-Space. One of ten structures is built around you, its Ultra Beast is placed inside, and an exit portal opens at a fixed point of the layout. Your overworld position is saved before you leave.

To come back, take the exit portal or fall into the void. Both routes return you exactly where you were standing, and the structure is torn down behind you.

The rules of the dimension

One player at a time. Ultra-Space is claimed for as long as you're in it, and no new wormhole will spawn anywhere on the server while it is. The claim survives a disconnect for five minutes, so a crash doesn't cost you your run — but if you don't come back in time, the slot is released and you'll be sent home on your next login.

Nobody dies in there. All damage is cancelled inside the dimension. No fall damage, no suffocation, no starving on a long hunt.

Nothing can be built or broken. The structure stays exactly as it was generated.

The Ultra Beast doesn't move, can't be hit, and never despawns. It's there to be caught, not fought with a sword — Cobblemon battles work normally.

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The ten structures

Each Ultra Beast gets its own arena, with its own spawn point, player arrival point and exit portal placement:

Nihilego · Kartana · Blacephalon · Pheromosa · Buzzwole · Guzzlord · Celesteela · Xurkitree · Poipole · Stakataka

Which one you get is random on every trip.

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Advancements

	How to earn it
Into the Unknown	Enter Ultra-Space for the first time
Ultra-Space Master	Catch every Ultra Beast

The second one tracks each species separately, so it fills in as you go.

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Commands

Command	Permission	What it does
/ultrabeasts info	all	Current spawn chance, as a ratio and a percentage
/ultrabeasts reload	OP level 2	Reload the config without restarting
/ultrabeasts wormhole spawn	OP level 2	Force a wormhole on yourself
/ultrabeasts wormhole clear	OP level 2	Clean up everything and free the dimension

wormhole spawn refuses if someone already holds Ultra-Space — the one-player rule applies to operators too.

wormhole clear is the panic button: it removes every wormhole and portal, sends anyone inside Ultra-Space back to their entry point, tears down the structure and releases the claim.

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Configuration

A file is created at config/cobblemon_ultrabeast/main.json on first launch:

{
  "WORMHOLE_SPAWN_CHANCE": 2000,
  "TRY_SPAWN_INTERVAL": 400
}

TRY_SPAWN_INTERVAL is how often the server rolls for a wormhole, in ticks. 400 is twenty seconds.

WORMHOLE_SPAWN_CHANCE is the denominator of that roll: 2000 means a 1-in-2000 chance each time. Together the defaults work out to roughly one wormhole per 11 hours of a single player being online — rare by design. Existing config files keep their own value: the default only applies to a new file.

Want to test? Set the chance to 1 and reload; you'll get a wormhole on the next interval. Out-of-range values are clamped rather than crashing, and the corrected value is written back to the file.

Run /ultrabeasts reload to apply changes without a restart.

Coming from 4.0 or earlier? Your old config/ultrabeasts.json is moved to the new location automatically on first launch, and renamed to ultrabeasts.json.migrated.

Client settings

Each player also gets config/cobblemon_ultrabeast/client.json, read by their own game only:

{
  "ENCOUNTER_CINEMATIC": true
}

Set ENCOUNTER_CINEMATIC to false to skip the arrival cinematic in Ultra-Space and get a short fade from black instead. It is read again on every trip, so no restart is needed.

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Installation

1. Install Cobblemon 1.8.4 or later for Minecraft 1.21.1.
2. Install the Kotlin bridge for your loader — Fabric Language Kotlin on Fabric, Kotlin for Forge on NeoForge. Cobblemon needs it.
3. Drop the Ultra-Beasts jar matching your loader into mods/.
4. Launch.

Dependencies

	Fabric	NeoForge
Minecraft	1.21.1	1.21.1
Cobblemon	1.8.4+	1.8.4+
Also required	Fabric API, Fabric Language Kotlin	Kotlin for Forge

A note on the world warning

Because the mod adds a custom dimension, Minecraft flags single-player worlds as using "experimental settings" and shows a confirmation screen on load. This is normal for any dimension mod and safe to click through. It does mean such worlds can't be uploaded to Realms.

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Server notes

Ultra-Space state lives in the world save, so a restart doesn't strand anyone: the structure, the exit portal and the current claim all survive it. If the exit portal ever goes missing while someone is inside — a chunk unload, a stray /kill — it's restored automatically within a second. The same goes for the Ultra Beast.

The wormhole check is throttled and exits early whenever anyone holds Ultra-Space, so its cost on the tick loop is negligible.

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Building

./gradlew build

Jars land in fabric/build/libs/ and neoforge/build/libs/. The -dev and -sources jars are build artefacts; ship the plain versioned one.

Standard Architectury multiloader layout: shared code in common/, loader-specific wiring in fabric/ and neoforge/. The project uses an access widener for a handful of vanilla display-entity methods, mirrored as an access transformer on the NeoForge side — both files need to stay in sync if you extend the spawn animation.

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Issues

Bug reports and suggestions go to the issue tracker. Please include your loader, your config/cobblemon_ultrabeast/main.json, and the server log rather than just the client one — most of this mod runs server-side.