1. Download Worms 4 Extreme Fusion pack and Uharc.
2. Open Uharc and extract Worms 4 extreme fusion pack.
3. Copy content from data/data of extracted archive to your worms 4 mayhem directory. You will have to replace files. Be sure to make backup of Data folder.
4. Next copy all files from Worms 4 Extreme Fusion ( but not ones in data, because you already copied)into your Worms 4 mayhem directory.
5. Play game