Here is the full list of all 12 Ragtag Adventurers achievements.
Defeat Shiro in Team mode.
Defeat Shiro in Solo mode.
Defeat Osselor in Solo mode.
Defeat Osselor in Team mode.
Defeat Leshnyak in Solo mode.
Defeat Leshnyak in Team mode.
Defeat Uth'wara in Solo mode.
Defeat Uth'wara in Team mode.
Defeat Wurstbrat in Solo mode.
Defeat Wurstbrat in Team mode.
Defeat Eldingar in Solo mode.
Defeat Eldingar in Team mode.