1. What Are MU Online Resolution & Window Mode Settings?

Resolution controls how many pixels the game uses (800×600, 1024×768, 1920×1080, etc.). Matching this to your monitor’s aspect ratio (4:3, 16:9, 16:10, ultrawide) makes the game look sharper and prevents stretching.

Window mode decides whether MU Online runs in fullscreen or in a resizable window. Windowed mode is perfect if you want to chat on Discord, browse, or stream while playing.

• Fullscreen (WindowMode:0) – Better immersion, often slightly better performance.
• Windowed (WindowMode:1) – Easier multitasking and alt-tabbing, ideal for streaming or dual monitors.

2. Before You Change MU Online Resolution

Before editing any files, quickly prepare the following:

• Close the game client completely – MU must not be running while you edit settings.
• Find your monitor resolution – On Windows, right-click desktop > Display settings to see it.
• Backup the config – Copy LauncherOption.if to LauncherOption_backup.if so you can restore it if something goes wrong.
• Use a proper editor – Notepad is fine, but Notepad++ makes things easier to read.

3. Where to Find LauncherOption.if in MU Online

1. Go to the folder where your MU Online client is installed (for example: C:\Games\MUOnline\).
2. Look for a file named LauncherOption.if in the main client directory (often next to the launcher EXE).
3. If you can’t see it at first:
   • Run the launcher once, close it, and check again (some launchers create the file after first run).
   • Use Windows search in the client folder for LauncherOption.if.
4. Right-click the file > Open with > Notepad (or Notepad++).

Inside this file you’ll find the two key lines:

• /DevModeIndex: – controls which resolution preset the game uses.
• WindowMode: – controls fullscreen vs windowed mode.

4. RESOLUTION SETTINGS (DevModeIndex)

The main resolution control for MU Online is DevModeIndex. Each number maps to a specific resolution preset. Many servers use this classic set of values:

/DevModeIndex: