Here is the full list of all 20 Assassins vs Pirates achievements.
Robin skin unlocked
Prince skin unlocked
Jack skin unlocked
Mariner skin unlocked
Ninja unlocked
Frosty skin unlocked
Punchface skin unlocked
Mojito skin unlocked
Keeper skin unlocked
Blackbeard unlocked
Santa skin unlocked
Bosun skin unlocked
Desmon skin unlocked
Rogue skin unlocked
Mr. Nobody unlocked
Drowner skin unlocked
Demon Skeleton skin unlocked
Shaman unlocked
Cupid skin unlocked
Voodoo skin unlocked