You install the IPA loader once, then dropping in mods is just copying DLL files.

2.1 Find your game folder

Inside that folder you'll see JetIsland.exe and the JetIsland_Data\ folder. (On Steam you can jump straight there via right-click the game → Manage → Browse local files.)

2.2 Install the IPA loader (one time)

1. Download the patched IPA build (IPA-3.4.1-ca30be3.zip) from this site's How to Install page or the JetIslandMods GitHub org.
2. Extract the contents of the zip into your game folder — the same folder as JetIsland.exe. You should now have IPA.exe sitting next to JetIsland.exe.
3. Drag JetIsland.exe onto IPA.exe. This patches the game so it loads plugins on launch. IPA also creates a self-updating launch shortcut so your game stays patched even after Steam updates it.
4. Confirm a Plugins\ folder now exists in the game directory (IPA creates it).

2.3 Install a mod

1. Download the mod from this site. It will contain a .dll (and possibly AssetBundle files + a README).
2. Put the .dll into the Plugins\ folder.
3. If the mod ships AssetBundles (e.g. a map), follow that mod's README for where the .unity3d files go — typically the game-side JetIsland_Data\StreamingAssets\ folder, since plugins load them from Application.streamingAssetsPath. Always defer to the individual mod's instructions for asset placement and any extra per-mod config.
4. Launch the game. The mod loads at startup.

2.4 Uninstall / revert a single mod

• Delete the mod's .dll from Plugins\ (and any AssetBundles it added). That's it — the mod is gone next launch.
• Well-behaved mods avoid writing to your save, so removing them is clean. For example, Modifier Unlock states plainly: "Simply delete the mod and your collection progress will return to normal!" If a mod's README warns that it touches your save, read it before installing.

2.5 Fully un-patch the game (remove IPA itself)

If you want the game back to 100% vanilla (e.g. for troubleshooting, or before reporting a bug to the dev):

• Hold Alt while dragging JetIsland.exe onto IPA.exe. This reverts the IPA patch, restoring the original executable.
• You can then delete the Plugins\ folder, IPA.exe, and the IPA support files.

If a Steam update ever leaves the game un-patched (plugins stop loading after an update), just re-run step 2.2.3 — drag JetIsland.exe onto IPA.exe again. The shortcut IPA creates normally handles this for you.