# How to add a custom weapon or boss to a game you own with universal-modder

Repo: [rehan-remade/universal-modder](https://github.com/rehan-remade/universal-modder) | Difficulty: Beginner | Time: 1 hour | Basis: Seen in the wild

Describe a new item or boss in plain words and have the agent build it, with art, and test it in the running game.

**Who it is for:** Terraria player who wants a homing missile launcher and a custom boss but has never written a mod

**The problem:** Writing a mod means learning the game's engine, code layout and asset formats before anything shows up on screen.

**The outcome:** A working mod with generated sprites, tested in the real game, plus a recorded showcase clip.

## Steps

1. Install the plugin for your agent, for example `/plugin marketplace add rehan-remade/universal-modder` then `/plugin install universal-modder@universal-modder` in Claude Code.
2. Store your fal key with `um fal key set` and start your agent with FAL_KEY set.
3. Tell the agent what to add, for example a homing missile launcher and a tactical nuke for Terraria, with sprites made by fal.
4. Let it run the mod-any-game loop: recon, read the code, build one slice, generate assets, verify in game.
5. Review the result and the showcase video it cuts.

## Prompt to paste into your agent

```text
Use universal-modder to mod <game name> installed at <path to game folder>: add <new item or boss>. Generate the art with fal, test it in the running game, and tell me which route and engine you used.
```

## Caveat

Targets games you own, single-player or offline only. The README says it refuses to bypass anti-cheat or write multiplayer cheats.

## Seen in the wild

- X (Oct 2026): https://x.com/i/web/status/2110084405306011842
- Reddit: https://www.reddit.com/r/ClaudeAI/comments/1wug3lx/new_opensource_project_tries_to_let_claude_code/

Dual-use notice: only use this on software, sites and systems you own or are authorized to test.

Disclaimer: Third-party repos we don't own or vouch for. AI-generated use cases can be wrong: review everything and run at your own risk. Full text: https://dedupedai.com/disclaimer/

URL: https://dedupedai.com/use-cases/rehan-remade-universal-modder/add-custom-items-to-owned-game/