You can add a Singleplayer button by creating a Button element and giving it an action.
Steps
- Open the layout editor.
- Right-click the background → New Element → Button.
- Right-click the new button → Edit Action Script.
- Add the action Open Screen or Custom GUI.
- Use the screen identifier for the Singleplayer screen.
If you don’t know the screen identifier yet, you can find it with FancyMenu’s Debug Overlay:
- Open the screen
- Enable Customization -> Debug Overlay
- Copy the identifier shown there
More info:
If you want, I can also tell you how to make the button look like a vanilla button. 🙂