Can the full file paths for step 2, step 3, step 4, step 6 be put in there? I think this is where I'm screwing things up (that I've got so many different file paths and I'm copying/replacing things in the wrong place. Thanks. Ok, so there's basically four directory trees you're dealing with. This is just the nomenclature I've made up in my head: 1. The "game tree", where the main files are installed. This is typically "~/Library/Application Support/Steam/SteamApps/common/XCom-Enemy-Unknown". (It will be in a different place if you told Steam to install the game somewhere else when you installed it.) It should have two subdirectories, "XCOMData" and "XCOM Enemy Unknown.app". Note that for Enemy Within, all the relevant files are in "XCOMData/XEW/XComGame". It's easy to get confused and drop them in "XCOMData/XComGame" by accident, in which case they won't do anything. 2. The "app bundle tree", meaning the .app folder that you can double-click to launch the game. This is the directory "XCOM Enemy Unknown.app" inside the game tree above. In the finder, to show this directory you've got to right-click on "XCOM Enemy Unknown" and select "show package contents." 3. The "feral tree", which lives in "~/Library/Application Support/Feral Interactive/XCOM Enemy Unknown". This directory probably won't exist until you've run the game at least once. The relevant files in here are all in the directory "XEW/MacInit". As above, don't forget the XEW part. 4. The "extract tree" is the directory where you extracted the mod files from the Windows installer with innoextract. It contains all the new files you're going to copy into the other places to install the mod. The files you want to deal with are all under the "app/XComGame" directory. So in Anderkent's steps above: 2. Replace .upk files, remove corresponding .upk.uncompressed_size The UPK files live in the game directory tree, under "XCOMData/XEW/XComGame/CookedPCConsole". In the extract tree, these live in "app/XComGame/CookedPCConsole". 3. Replace Localization files in two directories (under XComGame, and in MacOverrides near the binary) The files in Localization (in the extract tree: "app/XComGame/Localization/INT/*.int" from the Windows installer) need to be replaced in two separate directories: a. In the game tree: "XCOMData/XEW/XComGame/Localization/INT". b. In the app bundle tree: "XCOM Enemy Unknown.app/Contents/Resources/MacOverrides/XEW". 4. Replace Config files under XComGame The config files (in the extract tree at "app/XComGame/Config") go in the game directory tree at "XCOMData/XEW/XComGame/Config". 5. Delete files under MacInit in ~/Library/Application Support/Feral Interactive/blahblah These are all under "XCOM Enemy Unknown/XEW/MacInit" in the feral tree. 6. Move DefaultGameCore.ini to MacInit/XComGameCore.ini and DefaultLoadouts.ini to MacInit/XComLoadouts.ini (all the other files will be generated from XComGame/Config) Here you're copying and renaming files that you already copied during step 4. These two files live in the game directory tree in "XCOMData/XEW/XComGame/Config" and you're copying them to the feral tree at "XCOM Enemy Unknown/XEW/MacInit", and then renaming them as above. Alternately for step 6 you can just copy the files from the extract tree. Relative to the mod, they live in "app/XComGame/Config", and you'll be copying them into "XCOM Enemy Unknown/XEW/MacInit" in the feral directory and renaming them. Hope that is clear and helpful. At some point I will throw this up on a wiki page, but I'm having trouble logging into the wiki right now. in Step 5 what files I must delete also can someone explain step 8 ?