Friend's iMac finder not responding because of failed massive drag and drop?

[The Grim Ninja]

There's several different strategies for attack:

Can you do Target Disk Mode? Log in. Drag em to the trash.

Can you log into a different user? Log in. Drag em to the trash.

Can you boot from a different drive? Drag em to the trash.

Is file sharing active or can it be set active? Log in. Drag em to the trash.

Can you use other apps with bearable speed? Use terminal to delete the file types.