Like Mandrake the magician, Morg the end of Sky City needs to be nerfed. By the time I fled he had 25 protected -100% tower shields. An impossible number to remove. This stems from his ability to designated players as his chosen one and when they do anything but attack him he adds more shields.
It seems you need to create a special deck for this boss which lets you attack every round and literally kill him by paper cuts. Still not certain it could work.