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