The Hand of Merlin

You will need to unlock all the characters.  You can see the unlock requirements by hovering over their character in the inspect menu.   Most of them are very straight forward, the only 2 which require a bit of work are the one for killing three enemies in the same round, this has to be done by 1 of your characters (the description is not clear on this) and the other one is for getting to level 10.   See the "A Hero's Journey" trophy for an easy way to do this.