Cannot mount bootable Windows 10 drive
Let me know if anything goes wrong! I have tried to update everything for the latest version of VirtualBox, but I may have messed up somewhere...

The method I use relies on VirtualBox for its operation. Follow these steps:


Install the latest version of VirtualBox from https://www.virtualbox.org/wiki/Downloads. Make sure it installs the command line tools.
Once installed, open it and create a new VM by clicking "New" on the top left.
Select the type to be "Microsoft Windows", and select the version as "Windows 10 (64 bit)", then give it a name of your choosing.
Select "Do not add a virtual hard drive". We will be creating one on our own for our purposes. Click "Create".
If you have not created a partition for Windows, do so now in Disk Utility. Click on the disk (not any partition) in the sidebar, and click the partitions tab. Then click the "+" button, and make a new partition as large as you want it to be. 30GB is a good minimum size.
Now we have to open the Terminal. Type the following command: diskutil list. From the list of disks, make a note of the disk identifier in the last column that belongs to the partition you created for Windows. We will need this in the next step.
Run the command sudo chown $USER /dev/disk#s#. Replace disk#s# with the identifier from earlier. Enter your password and push return. Also run sudo chown $USER /dev/disk#s1. Use the same identifier, but replace the last number with a 1. Also run sudo chown $USER /dev/disk# using the first half of your identifier (minus the s# part).
Unmount the disk by typing diskutil unmount /dev/disk#s# using your identifier.
Now we have to create the disk for the VM to use for installation. Run the command VBoxManage internalcommands createrawvmdk -filename ~/RawWinDisk.vmdk -rawdisk /dev/disk# -partitions 1,#. Replace "disk#" with the appropriate first half of the identifier from earlier, and replace the second # sign with the last number in your identifier.
Unmount the disk again diskutil unmount /dev/disk#s#, using your identifier.
Now you should have a ".vmdk" file in your home folder. Go back into VirtualBox, select the VM you created, and click "Settings". Select the "Storage" tab, add an IDE controller by clicking the second "+" icon at the bottom, click on the "IDE" controller and click the second "+" sign directly to right of the controller (the hover text is "Add Hard Disk").
Click "Choose existing disk", and navigate to the VMDK we just created, which should be in your home folder. Click it and select "Open". Now you should see the newly added disk just below the "IDE" controller.
Click on "Empty" just below the "SATA" controller, check "Live CD/DVD", and click the little CD icon next to "SATA Port #".
Click "Choose Virtual Optical Disk File...", navigate to your ISO, and open it.
Start the VM and install windows on the 30G partition.
When the installation is done and you're logged in, shut down Windows and you should see the disk created by Windows appear on the desktop. You can get the Boot Camp drivers for your laptop from https://support.apple.com/kb/DL1720?locale=en_US. Put this on a flash drive formatted as ExFAT or FAT so Windows can read it.
You should now be able to reboot into Windows by holding alt down, or selecting the disk in Startup Disk preferences.


Make sure you update your BootCamp with Apple Software Update once you have BootCamp installed on the Windows side. These are technically Windows 8.1 drivers, which should work well enough for you to at least connect to the internet and get the latest version.