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According to a post on the PlayStation Blog from developer Monolith Productions' Community Manager Andy Salisbury, preordering the game for PS4 will get you the PlayStation Legion Edition missions. The exclusive missions will have you battling two more Warbands in Mordor: the Blood Hunters and the Flesh Burners.
http://www.gamespot.com/articles/middle-earth-shadow-of-mordor-gets-ps4-exclusive-m/1100-6421773/