Sonic Mania Decomp: Three Retail Versions and a Built In Mod Loader

By Indie Kings | October 28, 2026

Updated October 28, 2026: RSDKModding/Sonic-Mania-Decompilation, a complete decompilation of Sonic Mania, builds three distinct retail versions from one source tree: 1.00, the initial console release, 1.03, the initial PC release, and 1.06, the Plus update. The repository dates to February 13, 2020, has 826 stars, 202 forks and 14 contributors, and its newest commit, from May 12, 2026, fixed a mislabeled type variable in the animal spawning code.

Image: a Sega Genesis 3, the later budget revision of the hardware Mania's visual style calls back to, via Wikimedia Commons.

Three versions, one tree

Most decompilations pick a version and commit to it, because matching one binary is already a full time problem. Sonic Mania's project supports three. Version 1.00 was the initial console release, 1.03 was the initial PC release, and 1.06 arrived with Sonic Mania Plus, the expanded edition that added playable characters and remixed stages. The README lists them as supported build targets, and the build system can target RSDKv5Ultimate rather than standalone RSDKv5, which is the same engine revision the Plus era games use.

Supporting three versions is a statement about what the project is for. A preservation effort only needs the version that shipped most widely. A modding base needs the version people actually run, and in Mania's case that depends on whether a mod was written against the original release or the Plus update. Because the differences between those builds are not cosmetic, the project has to keep the older code paths alive instead of simply moving forward. The practical result is that someone with a 1.03 install and someone with a 1.06 install can both build from the same repository and get a working game, which is a more generous arrangement than most fan projects attempt.

Assets, saves and the Netflix exclusion

The repository contains code, not content. The README is direct about the requirement: without assets from an official release, the decompilation will not run, and it lists Steam, the Epic Games Store, Switch, PlayStation 4 and Xbox One as legitimate sources. It also rules one source out explicitly. The Netflix Games version is not supported, a sentence that would have been unnecessary a few years ago and now reflects how many ways the same game can be packaged. The warning against piracy is equally direct, and the project credits Sega, Headcannon and Evening Star as the reason it exists at all.

Saves are the more interesting detail. The README notes that a save from the official PC version can be carried over by copying the savedata into the folder that contains the decompilation. That sounds trivial and it is not: it means the file formats and directory expectations have been reconstructed accurately enough that the original game's data is readable without conversion. For players, it removes the usual friction of trying a fan build and losing progress. For modders, it means testing can start from a real save rather than a fresh file, which shortens the loop between an edit and a result. The mod loader and API, with their save redirection, build on the same foundation.

Fourteen people, six years

Fourteen contributors over six years is a small number, and it explains the project's tempo. The repository was created in February 2020, the newest default branch commit is dated May 12, 2026, and GitHub records a push on October 20, 2026, which typically means branches or tags moved even if the main line did not. Twelve issues are open. For a decompilation of a 2017 game that has already been rebuilt to a working state, that profile reads as maintenance rather than development: the hard matching work is done, and what remains is the occasional correctness fix like the animal spawning variable that was mislabeled.

Small teams also shape what gets documented. The build instructions assume CMake and vcpkg on Windows, with a warning not to download the source ZIP because it omits the submodules, and they spell out the dependency install commands for each major Linux distribution. That level of detail is written by people who have answered the same question repeatedly. It is not glamorous, and it is the difference between a repository that a newcomer can build in an afternoon and one that produces a stream of issues from people who gave up at the toolchain step.

Project card

Item	Detail
Repository	RSDKModding/Sonic-Mania-Decompilation on GitHub
Game	Sonic Mania, built on Retro Engine v5Ultimate
Created	February 13, 2020
Supported versions	1.00 console release, 1.03 PC release, 1.06 Plus update
Engine target	Can build against RSDKv5U rather than standalone RSDKv5
Assets	Required from an official release, Netflix Games version not supported
Save transfer	Official PC savedata can be copied into the decompilation folder
Build	CMake, vcpkg on Windows, recursive clone required for submodules
Latest commit	May 12, 2026, mislabeled type variable in Animals_Create
Scale	826 stars, 202 forks, 14 contributors, 12 open issues

FAQ

What is the Sonic Mania decompilation?
A source reconstruction of Sonic Mania's game code that builds a playable game when combined with assets from an official release.

Which versions can it build?
1.00, the original console release, 1.03, the original PC release, and 1.06, the Sonic Mania Plus update.

Does it include the game's assets?
No. The README requires assets from Steam, Epic, Switch, PS4 or Xbox One, and states that the Netflix Games version is not supported.

Can I keep my save?
Yes. Copying the official PC version's savedata into the decompilation's folder carries progress across.

What does the mod loader add?
A built in loader and API for mods, including save redirection and XML based asset loading, so mods can be installed without patching the base install.

Is it still updated?
The newest commit is from May 12, 2026, and the repository was pushed to on October 20, 2026. Twelve issues remain open.

Bottom Line

Three supported versions is the detail that separates this project from a proof of concept: it accepts that people own different builds of Mania and refuses to make them choose. The save compatibility is the quiet proof that the reconstruction is accurate, and the Netflix exclusion is a reminder that even a 2017 game keeps reappearing in new packaging. With 14 contributors and the main matching work behind it, this is now a maintenance project, and maintenance is exactly what a modding scene needs from its foundation.

Sources

GitHub RSDKModding/Sonic-Mania-Decompilation README, supported versions, asset requirements, save transfer and build notes, accessed October 28, 2026
GitHub API metadata for Sonic-Mania-Decompilation, stars, forks, contributors, issues and latest commit, accessed October 28, 2026