If you decide to proceed, use the link mentioned above (search for "Platinmods MU Origin Offline v8.0") as it has the most active community support. Always, always back up your device before installing any third-party APK.
"They trapped us when the official servers died. This offline APK is a lifeboat. Don't close the app. You’re the new host." mu offline android link
Once you successfully install from a working , the gameplay differs significantly from the official MMO. If you decide to proceed, use the link
This blog post outlines how you can relive the classic experience on your Android device without needing a constant internet connection. If you decide to proceed