Here is the full list of all 14 By Any Means Necessary achievements.
Defeated the Killer Spider in the Valerian ship.
Defeated all the monsters in the Pet Arena.
Defeated all the monsters of the Pet Arena dungeons.
Completed all the monster hunting quests in the Norsfolk Swamp.
Found the Judgment ability scroll.
Found the Meteor ability scroll.
Found the Celestes secret dungeon.
Found Yusef's ultimate weapon.
Found Ira's ultimate weapon.
Found Gedge's ultimate weapon.
Found Juba's ultimate weapon.
Found Adelaide's ultimate weapon.
Found Devon's ultimate weapon.
Completed your mission by any means necessary.