The recent update to Hollow Knight, version 1.5.12620.0, has left much of the modding community in a state of flux. If you launched your game recently only to find your custom skins missing, your Randomizer not loading, or Lumafly giving you a cryptic error message, you are not alone. The short answer to the question of whether mods work on Hollow Knight 1.5.12620.0 is: not officially, and not without significant manual intervention.

Standard modding tools like Lumafly and Scarab do not currently support this specific version. This update was not a typical bug-fix patch; it introduced fundamental engine changes that moved the game to Unity 6 and D3D12. These changes effectively broke the hooks that modders use to inject code into the game.

The Technical Shift Behind Version 1.5.12620.0

To understand why your mods no longer work, it is necessary to look at what changed under the hood. For years, Hollow Knight modding relied on a relatively stable version of the Unity engine. Modding APIs (Application Programming Interfaces) function by wrapping around the game's core files—specifically the Assembly-CSharp.dll—to allow community-created code to run alongside Team Cherry's original scripts.

Version 1.5.12620.0 updated the game to a much newer version of Unity. While this update improves performance for some modern hardware and fixes long-standing engine-level bugs, it renamed internal methods, changed how memory is managed, and altered the rendering pipeline. When an existing mod tries to find a specific function to trigger a custom animation or change a damage value, that function either no longer exists where it used to be or has been renamed.

Furthermore, the shift to D3D12 as the default rendering API has caused compatibility issues with visual mods. Overlay mods that display health bars or specialized UI elements often rely on specific shaders that are not currently compatible with the new rendering setup.

The Most Stable Solution: Downpatching

For the vast majority of players who want to jump back into a modded playthrough of Godhome or start a new Randomizer run, the best course of action is downpatching. Downpatching involves reverting your game to a previous version that is still supported by the stable releases of Lumafly and the Modding API.

Reverting on Steam

Steam makes this process relatively straightforward through its "Betas" system. During our tests, reverting to version 1.5.78 proved to be the most effective way to restore mod functionality without losing significant game features.

  1. Open your Steam Library and find Hollow Knight.
  2. Right-click the title and select Properties.
  3. Navigate to the Betas tab on the left side of the window.
  4. In the "Beta Participation" dropdown menu, look for a version labeled 1.5.78 or 1.4.3.2.
  5. Once selected, Steam will automatically download the necessary files to revert your game.

After the download finishes, you can launch Lumafly. You may need to point the installer to your game directory again to ensure it recognizes the older executable. Once the Modding API is re-installed on this stable version, your mods should load exactly as they did before the 1.5.12620.0 update.

Why 1.5.78 and Not 1.4.3.2?

While many old-school guides recommend 1.4.3.2, version 1.5.78 is generally preferred for modern modding. It includes the native 64-bit support and various quality-of-life updates that Team Cherry implemented, while still maintaining compatibility with the current stable builds of the Modding API. Only use 1.4.3.2 if you are trying to run specific, very old mods that were never updated for the 1.5 series of patches.

The Experimental Path for Version 1.5.12620.0

For those who are determined to keep their game on the latest version—perhaps to benefit from the Unity 6 performance improvements or simply to avoid the hassle of downpatching—there is an experimental route.

The Hollow Knight modding community is incredibly active on platforms like GitHub, and work has already begun on an unofficial Modding API designed specifically for version 1.5.12620.0. However, this is not a "click and play" solution.

Manual API Installation

Using these experimental builds requires manual file manipulation. In our practical testing, we found that even with the experimental API, many popular mods still fail to load because they require updates to their own individual codebases to match the Unity 6 changes.

If you choose this path, you will typically need to:

  1. Locate your Hollow Knight installation folder (usually under steamapps/common/Hollow Knight).
  2. Navigate to hollow_knight_data/managed.
  3. Back up your original Assembly-CSharp.dll.
  4. Replace it with the experimental version provided by community developers on GitHub.
  5. Manually create a Mods folder and place your .dll mod files there.

Warning: This method is highly unstable. We experienced multiple crashes during room transitions and encountered "Black Screen" errors when trying to load specific charms. Only proceed with this if you are comfortable troubleshooting and have backed up your save files.

Impact on Popular Mods

Not all mods are affected equally by the version 1.5.12620.0 update, but the most popular ones are currently in a state of broken compatibility.

Hollow Knight Randomizer

The Randomizer is one of the most complex mods available, touching almost every aspect of the game's item and room logic. Because it relies heavily on specific map triggers and item acquisition scripts, it is completely non-functional on the new version. The developers of Randomizer 4 are aware of the update, but a full port to the Unity 6 environment will take time.

Debug Mod and Cheats

The Debug Mod, which allows for invincibility, noclip, and item spawning, is also broken. The UI for the Debug Mod often fails to render under the new D3D12 pipeline. While some basic cheats might still work if manually injected, the overlay that makes the mod usable is currently incompatible.

Custom Knight (Skins)

Visual skin mods are perhaps the most missed feature. These mods work by replacing sprite sheets in the game's memory. With the engine change, the way Hollow Knight handles sprite loading has shifted, meaning even if you manage to install the mod, the Knight might appear as a glitchy box or not change at all.

Protecting Your Save Data During Version Changes

One of the biggest risks when dealing with version 1.5.12620.0 and modding is save file corruption. Hollow Knight saves are located in the AppData/LocalLow/Team Cherry/Hollow Knight folder.

When you move from 1.5.12620.0 back to 1.5.78, the game may attempt to read save data that contains information from the newer engine version. To prevent losing your 112% completion file, follow these steps:

  1. Press Win + R and type %appdata%.
  2. Go up one level to the LocalLow folder, then enter Team Cherry and Hollow Knight.
  3. Copy all files ending in .dat (e.g., user1.dat) to a safe location on your desktop.
  4. If a modded run fails, you can delete the corrupted files and paste your backups back into the folder.

Troubleshooting Common Modding Failures

If you have downpatched but your mods still won't load, consider these common points of failure that we encountered during our setup:

Administrator Privileges

Mod installers like Lumafly need permission to write files into the Steam directory. If you are running Steam inside the Program Files folder, Windows Defender often blocks the modder from overwriting the Assembly-CSharp.dll. Always run your mod installer as an Administrator.

Antivirus False Positives

Because modding tools function similarly to how a virus might (by injecting code into an existing executable), antivirus programs frequently flag them. You may need to add an exclusion for the Hollow Knight folder and the Lumafly.exe to ensure the files aren't quarantined.

Incorrect Folder Structure

A common mistake is placing mods inside a sub-folder within the Mods directory. Most Hollow Knight mods should exist as a single .dll file directly inside hollow_knight_data/managed/mods. If they are buried inside another folder, the API will likely skip them during the boot sequence.

Will Official Support Ever Return for 1.5.12620.0?

It is highly likely that the community will eventually update the standard tools to support this new version. However, because this was a major engine overhaul, it is not a simple fix. The modding team behind Lumafly and the core API are volunteers who must rewrite significant portions of their code to accommodate Unity 6.

Until a stable version of the Modding API is released for 1.5.12620.0, downpatching remains the "Gold Standard" for anyone who wants a hassle-free experience.

Summary of the Current Situation

To recap the current state of Hollow Knight version 1.5.12620.0 modding:

  • Standard Compatibility: Broken. Lumafly and Scarab do not support this version yet.
  • The Cause: A major engine update to Unity 6 and D3D12 that changed internal code structures.
  • Best Fix: Use the Steam Betas tab to downpatch your game to version 1.5.78.
  • Experimental Fix: Manual installation of community-made API builds from GitHub, though this is unstable and not recommended for most.
  • Save Security: Always backup your .dat files before changing versions or installing experimental mods.

Frequently Asked Questions

Can I mod Hollow Knight on console version 1.5.12620.0?

No. Modding is strictly limited to the PC versions of the game (Steam, GOG, and Game Pass). Console platforms like PlayStation, Xbox, and Nintendo Switch do not allow the file injection required for these mods to function.

Does the GOG version have the same problem?

Yes. The 1.5.12620.0 update was rolled out across PC platforms. If your GOG version has updated, you will face the same modding hurdles. GOG Galaxy allows for version rollbacks similar to Steam, which you can access via the "Manage Installation" and "Configure" menus.

Why did Team Cherry update the engine so late?

While Team Cherry has not released a detailed statement, engine updates are often necessary to ensure the game continues to run on future versions of Windows and macOS, and to take advantage of better controller support and performance optimizations provided by newer Unity versions.

Will using mods on version 1.5.12620.0 ban me from Steam?

No. Hollow Knight is a single-player game, and Team Cherry has historically been very supportive of the modding community. There is no anti-cheat software that will result in a Steam ban. However, be aware that modding can sometimes disable Steam Achievements, so if you are hunting for "Steel Heart" or "Speedrun 2," it is best to do so on a clean, unmodded install.

How do I know if my downpatch worked?

Launch the game and look at the bottom left or top left corner of the main menu screen. It should display the version number. If it says 1.5.78 and you see the Modding API version listed, your downpatch was successful and your mods should be active.

My game shows a black screen after installing the experimental API. What now?

This is a common conflict with the new rendering pipeline. Try adding the launch option -force-d3d11 in Steam. Right-click Hollow Knight > Properties > General > Launch Options. This forces the game to use the older DirectX 11, which is often more compatible with experimental mod builds.

Where can I find the latest updates on mod compatibility?

The best place to stay informed is the official Hollow Knight Discord server, specifically the #modding-announcements and #modding-help channels. The developers of the API post regular updates there regarding version compatibility.

Can I use my 1.5.12620.0 save on a downpatched 1.5.78 version?

Usually, yes. Hollow Knight's save format is backwards compatible for the most part. However, some minor glitches might occur if you saved your game in an area or state that was specifically changed by the new update. Always keep a backup before attempting to load the save.