Do I need the original game files to run Undertale Decompilation?

Yes. The project does not include the original game's assets, so you need your own copy.

Can I use this without owning the Switch or Xbox version?

Yes. Any version you own should work, but Switch- or Xbox-exclusive content will be missing and replaced with placeholder assets.

Undertale Decompilation

DecompilationHalted

Source code reconstructed from the original game's compiled binary, so the game can be understood, rebuilt and ported.

Based on Undertale

compare all 3 clones

Image of the original game, Undertale. This project has no screenshots of its own yet.

Undertale (original game, not this project) — Image of the original game, Undertale. This project has no screenshots of its own yet.

Links, repository & details

About

Undertale-DC is a decompilation of the latest version of UNDERTALE for the Xbox One, ported to the latest GameMaker Studio 2 Beta with many toggleable enhancements. It offers a main branch with enhancements and bug fixes, and a vanilla branch with the decomp-exclusive features and enhancements removed.

How it differs from the original

If you only own a version other than Switch or Xbox, Switch or Xbox exclusive content is replaced with placeholder assets.

Getting started

You need your own copy of UNDERTALE; the Xbox version is highly recommended and the Switch version is the closest alternative. Clone the repository, run the setup script to import the game's assets from your copy, then open the project file in the latest GameMaker Studio 2 beta.

Known issues & limitations

Without the Switch or Xbox version, their exclusive content is replaced with placeholder assets.

What you need to run it

Original game files required. The project ships code only; you provide your own copy of the game (Xbox version).

You need to own a copy of the game; any version is supported, though the Xbox version is highly recommended.

Features

The main branch includes enhancements and bug fixes for a stable, improved modding and playing experience.
The vanilla branch removes decomp-exclusive features and enhancements for a more vanilla modding experience.

Summarised from the project's README.

FAQ

What is Undertale Decompilation?: Undertale Decompilation is an open-source decompilation of Undertale. Source code reconstructed from the original game's compiled binary, so the game can be understood, rebuilt and ported. The original game ran on Xbox.
Do I need the original game files to run Undertale Decompilation?: Yes. The project does not include the original game's assets, so you need your own copy.
Can I use this without owning the Switch or Xbox version?: Yes. Any version you own should work, but Switch- or Xbox-exclusive content will be missing and replaced with placeholder assets.