1 and 2) I've got God of War and Deimos by finishing on Hard. 3) Buy the orb worth 250,000 in Temple of Zeus for a robot. 4) Finish the Temple of Zeus and go to the secret passageway. This costume only works on Combat Arena. 5) Finish the game on God Mode for Ghost of Sparta. 6) There's another one that I guess you get by finishing all of the challenges, haven't got it yet.