Well when I was in wizard City exploring my friend asked me for help so I teleported to her and she was battling Grendels. There was about four of them and when I got a attack card ( Balance specificly ) and I clicked on the fourth Grendel nothing happended and it would not let me attack or anyhing on only that grendel unless I used a attack all targets spell. Is this a bug or just my computer?
Either the Grendel hadn't actually joined the battle for that turn or perhaps your friend had used Beguile on it. If an enemy is Beguiled it is like it is on your team and it cannot be targeted with an attack or trap.