The Underworld Mod
by sr_steve
The Underworld Mod adds a large dungeon built from custom blocks, plus swords and a shield that apply effects to whatever they hit, for NeoForge on 1.21.8.
What it does
The dungeon is the core of the mod. It consists of a massive set of rooms made from new custom blocks, and each Underworld Chamber holds its own challenges. Some rooms are larger than others, and a boss sits at the end of the route. Players can only find the dungeon in the world, so most of the new items, including the special swords and decorative pieces, are reached through it.
The weapons are the other half of the mod. The Knife is a small dagger with a very fast attack speed that compensates for its low damage. The Blood Dagger causes Bleeding for 10 seconds on any entity it hits. The Ice Blade stuns targets with Freezing. The Heavy Mallet attacks slowly but deals extremely high damage. The Lightning sword strikes a lightning bolt on each hit, and the Flaming Hielaman shield sets attackers on fire for 15 seconds.
The mod is server-side only, so players join a server running it without installing anything. It is published for NeoForge on 1.21.1 – 1.21.8, with 1.0 for 1.21.8 as the latest file, and All rights reserved applies, so the mod is not open source.
Key features
Massive custom dungeon
A large dungeon made from new blocks, with rooms, challenges and a route that ends in a boss.
Special swords
Swords such as the Lightning and Ice Blade each apply an effect to the entity they strike.
Blood Dagger bleeding
The Blood Dagger inflicts Bleeding for 10 seconds, dealing damage over time to the target.
Flaming shield
The Flaming Hielaman shield sets whatever it blocks on fire for 15 seconds.
Gallery
Compatibility
Latest build for each game version and loader.
Only full game releases are shown. This mod publishes no snapshot builds.
How it compares
Lunar Swords is a NeoForge mod for 1.21.1 – 1.21.8 that needs client and server, under the Apache License 2.0, so every player must install it. Squarby's daggers is a server-side only NeoForge mod for 1.21.1 – 1.21.3 under All rights reserved, so it covers a shorter version range than this mod. The Dungeon Experience also needs client and server and is released under Creative Commons Attribution 4.0, for 1.21.1 only.
| Mod | Loaders | Game versions | Environment | Updated |
|---|---|---|---|---|
| The Underworld Mod | NeoForge | 1.21.1 – 1.21.8 | Server-side only | 2025-07-20 |
| Lunar Swords | NeoForge | 1.21.1 – 1.21.8 | Client and server | 2026-08-02 |
| Squarby's daggers | NeoForge | 1.21.1 – 1.21.3 | Server-side only | 2024-10-31 |
| The Dungeon Experience | NeoForge | 1.21.1 | Client and server | 2026-07-28 |
Questions
Does the Underworld Mod need to be installed on clients?
Where are the special swords found?
Which game versions does the Underworld Mod support?
In the catalog
The Underworld Mod is one of 19,031 Adventure mods on ModsFinder, and one of 8,588 Adventure mods for NeoForge. 17,695 mods support Minecraft 1.21.8.
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What the author says
The Underworld Mod is a mod that revolves around a new dungeon made out of new blocks and containing new challenges inside. The dungeon is also the only place you cant find most things added by the mod, including special swords with effects and decorative items. I plan to add even more swords with effects, and make…
Official listing
- Modrinth page
- modrinth.com/mod/the-underworld-mod
- Owner
- sr_steve
- Published
- 2025-01-22
- Updated on Modrinth
- 2025-07-20
- Facts verified
- 2026-10-15