Some mods need to be above or below others. For example, a model swap usually goes above a level retexture. When in doubt, disable all mods and enable them one by one to find the conflict.
Many gameplay or visual mods require SonicGMI (Generations Mod Injector) or CodeLoader . Read the mod’s description carefully. If it says “requires CodeLoader” and you don’t have it, the mod will silently fail. sonic generations mods not working
If vanilla Generations runs fine but mods break it, right-click the game in Steam → Properties → Installed Files → Verify integrity of game files. This fixes missing DLLs or corrupted archives. Some mods need to be above or below others
The original game doesn’t support mods natively. You must use HedgemodManager (not the old SonicGLVL or other deprecated tools). Make sure you’re on the latest version. Many gameplay or visual mods require SonicGMI (Generations