Have finished the storyline and have just been running around collecting the rest of the collectables.
Last collectable I have is in the "dream" area, Asguard.
There is one collectable that requires a key, which I need to get from any enemy.
My issue is that all the enemies in this area are "friendly" and therefore unkillable.
I have tried the usual restart game, restart console, reload save, wake from dream area and re-enter but nothing seems to change the status of the enemies.