Guide · Agent skill
How to use the Mashups: Combine Two Games agent skill
Updated · written with AI from the project's own documentation and checked against our catalogue data
The mashup-mods skill is a planning guide for an AI agent that is building a mod merging two video games, such as Minecraft mechanics in Skyrim or an enemy from one game placed into another. It tells the agent which of several build patterns to use, how the two games should exchange data, and how to prove the mashup works before adding features. This guide shows you how to install it, how to ask for it in plain language, and what to expect from it.
Mashups: Combine Two Gamesrehan-remade/universal-modder · MIT Download the skill Quick start
- 1Download the skill. Download the mashup-mods ZIP from this page.
- 2Unzip it into a skills folder. Unzip into ~/.claude/skills/ for personal use, or into a project's .claude/skills/ folder.
- 3Or upload it in the Claude apps. Open Settings, go to Capabilities, then Skills, and upload the skill.
- 4Ask for a cross-game idea. Describe the enemy, mechanic or world you want to bring from one game into another.
- 5Answer the guest-game question. Say whether you want the guest's real behaviour or only its look or one mechanic, so the agent can pick the lightest route.
- 6Review the plan and contract. Check the chosen route, the data contract in docs/CONTRACT.md and the first test before any feature work.
What the skill makes the agent do
The skill covers passthrough mods, where two games run at once and exchange state, rendering and collision data. It also covers porting one game's content or mechanics into another, embedding a decompiled game as a library, and clean reimplementations that read the user's own game files.
Its main job is to stop the agent from jumping straight into code. It asks the agent to pick the lightest approach that delivers the idea, write down the data contract between the games, and define a first test that proves the mashup works.
- Choose a route: copy content, run both games at once, or rebuild part of a game.
- Write a contract covering player ownership, units, channels, protocol version and lifecycle.
- Pick a first slice and the check that proves it before building features.
- Record the route and reasons in MODLOG.md and tell the user what every player will need to own and install.
How to install the mashup-mods skill
Download the ZIP of the skill from this page. Unzip it so the skill folder sits in ~/.claude/skills/ to make it available to you across projects, or in a project's .claude/skills/ folder to limit it to that project.
If you use the Claude apps instead, open Settings, go to Capabilities, then Skills, and upload the skill there.
- Personal install: unzip into ~/.claude/skills/.
- Project install: unzip into the project's .claude/skills/ folder.
- Claude apps: Settings → Capabilities → Skills, then upload.
How to trigger the skill with natural requests
You don't need a special command. The skill is meant to activate when you ask for a cross-game idea. Phrases like combining two games, bringing an enemy, mechanic or world from one game into another, or rebuilding a game's runtime match its description.
Be specific about what you want from the guest game. The skill's first step asks whether you want its real behaviour, such as physics, inventory or combat, or only its look or a single mechanic, because that decides whether the guest has to run at all.
- Try: Build a mod that brings Minecraft blocks into Elden Ring as items.
- Try: I want an enemy from one game to appear in another. Plan the lightest way to do it.
- Try: Plan a mashup where two games run at once and share player position and collision.
Examples of what the skill helps plan
The skill describes the pattern behind viral mashups such as skateboarding in MW2 or Minecraft inside Skyrim. For a simple content port, such as adding a creeper-like enemy to a different game, it points to reimplementing the guest's behaviour in the host's mod API rather than running the guest.
For a two-game build, it walks the agent through guest process, transport on 127.0.0.1, host injection, back-channel collision and sync, and recommends starting with a single cube drawn in the other game before attempting real content.
- Port content: new enemies, weapons or block types that imitate the guest game.
- Passthrough: two processes exchanging state and drawing guest objects inside the host's render pass.
- Embedded library: a decompiled game used as a component of the host.
- Reimplementation: the guest's rules rebuilt headless inside a real host.
What you need before using it
The skill file itself is a planning guide. Its listing says it runs no scripts and uses no network. For the full workflow, the repository must include references/mashup-cases.md and the knowledge/techniques/ files, and the agent can search notes with the um command-line tool using um kb search.
The guidance assumes you already know engines, loaders, IPC and graphics APIs. Players of the finished mashup need to own both games and install the required host and guest software on their operating system.
- Files: SKILL.md and references/mashup-cases.md, plus the knowledge/techniques/ files for the full workflow.
- Optional tool: the um command-line tool, for um kb search.
- Experience with modding engines, loaders and graphics APIs.
- Legal copies of both games on the player's own machine.
um kb searchSafety notes: scripts, network and assets
The skill does not run scripts and does not use the network, according to its listing. Mashups it helps design may open local connections on 127.0.0.1 between processes, so review any code the agent writes before running it.
The skill is firm that assets must not be copied from the guest game into the mod. Converters should read the user's own install at runtime or install time, or the agent should recreate lookalike assets. Do not distribute mashups that contain copyrighted game assets.
- Read generated code before running it, especially anything that opens local ports or shared memory.
- Keep the guest's files out of the mod and read them from the user's own install.
- Check that the skill's referenced files are present before relying on the full workflow.
Tips for getting useful output
Ask the agent to name the closest prior project in references/mashup-cases.md before it chooses a route. Treat claims in other projects' READMEs as the creator's report until you have run them yourself.
Ask for the contract in docs/CONTRACT.md and the first slice before any features. Most of these projects fail by drifting out of sync, not by lacking code, so a clear test early saves time.
- Ask for the chosen route and reasons to be written into MODLOG.md.
- Ask the agent to explain where its plan differs from the nearest prior project.
- Start small: one object, then positions every frame, then collision, then real content.
What people use it for
- Porting a creature or weapon from one game into another as new content that imitates the original.
- Planning a two-game passthrough where a guest game renders inside the host's scene.
- Designing a headless reimplementation of one game's rules inside a real host.
- Documenting the data contract, units and failure handling before building a cross-process mod.
Frequently asked questions
How do I install the mashup-mods agent skill?
Download the ZIP from this page and unzip it into ~/.claude/skills/ for personal use, or into a project's .claude/skills/ folder. In the Claude apps, you can instead go to Settings, Capabilities, then Skills, and upload it.
Does the mashup-mods skill require any special software?
The skill file needs no scripts and no network access, per its listing. The full workflow expects references/mashup-cases.md and the knowledge/techniques/ files to be present, and it can use the um command-line tool with um kb search. Players of the finished mashup need to own both games and install the host and guest software.
Is the mashup-mods skill free?
The skill is listed under the MIT licence. Check the licence file in the repository for the terms that apply to your use.
What is the difference between a passthrough mod and a content port?
A content port adds new host content that imitates the guest, with no second game running. A passthrough mod runs both games at once, exchanges state, and draws guest objects inside the host's rendering, which is more complex.
Can the skill help me make a mod that combines Minecraft and another game?
Yes, the skill covers combining two games, such as Minecraft inside Skyrim, and recommends the lightest route that delivers your idea. It also says to plan the tests and data contract before writing code.
Why does the skill say not to copy game assets into a mod?
The skill states that assets must come from the user's own install and must not be copied into the mod. Converters should read files from the user's install at runtime or install time, or the agent should create lookalikes.
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Our verdict
Use this skill if you are an experienced modder or developer who wants a structured plan before building a mashup of two games, especially one involving cross-process data exchange. Pick something else if you only want a simple cheat or a single-game mod, or if you are new to modding, since the guidance assumes knowledge of engines, loaders, IPC and graphics APIs.
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