Here is the full list of all 12 Band of Outlaws achievements.
Saved all of the Merry Men
Beat the Guy of Gisborne
Beat the boss of Yorkshire
Unlocked a "Super" outfit
Beat the boss of Norfolk
Unlocked Fox Hood...Please don't sue........
Beat the Sheriff of Nottingham
Unlocked the Robyn outfit
Beat the boss of Loxley
Unlocked the Classic Robin outfit
Beat the boss of Rochdale
Unlocked the Scot outfit