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