android x86 6.0 doesn't support mouse integration?
The solution from Android X86 – No Mouse Cursor in Oracle VirtualBox:


  
  Make sure the VM is not running (powered off)
  Click on the VM name in the list (e.g., Android X86)
  Click Settings
  Click on the System category
  Make sure you’re on the Motherboard tab
  Change Pointing Device to PS/2 Mouse