Here is the full list of all 55 Disgaea 2 PC achievements.
Defeated all EX bosses!
Dealt 100,000,000 damage!
Defeated the Extra Boss "Pringer X Go"
Obtained the Yoshitsuna!
Obtained LV 9,999!
Cleared Extra Stage "Evil Academy Special Class!"
Dealt 10,000,000 damage!
Reincarnated 10 times
Entered the Land of Carnage for the first time
Defeated the Extra Boss "Item God"
Obtained Total LV 10,000
Defeated the Extra Boss "Laharl"
Defeated the Extra Boss "Flonne"
Defeated the Extra Boss "Protype Kurtis"
Defeated the Extra Boss "Kurtis"
Dealt 1,000,000 damage!
Defeated the Extra Boss "Baal"
Cleared Extra Stages "Cave of Ordeals"
Defeated your first pirate in the Item World
Unleashed Magichange 2
Defeated the Extra Boss "Zetta"
Cleared 100% of the Dark World stages
Cleared 50% of the Dark World stages
Cleared 20% of the Dark World stages
Unlocked the Dark World
Saw Bad Ending 2
Defeated the Extra Boss "Marjoly"
Saw the Tink ending
Obtained Total LV 5,000
Dealt 100,000 damage!
Defeated the Extra Boss "Prism Ranger"
Obtained 99 felonies
Obtained LV 1,000!
Saw Bad Ending 1
Defeated the Extra Boss "Priere"
Defeated the Extra Boss "Asagi"
Saw the Laharl ending
Defeated the Extra Boss "Mid-Boss"
Saw the Etna ending
Earned 10,000,000 HL from a single battle
Completed Ch. 4 of Axel's Story "The Dark Hero!"
Performed your first reincarnation
Performed your first Peta spell
Completed Ch. 1 of Axel's Story "The Evil Rangers"
Performed your first Magichange
Completed Final Chapter "The Truth"
Obtained LV 100!
Killed 1,000 enemies!
Obtained 1,000,000 HL!
Completed Ch. 10 "The Two Ninjas"
Completed Ch. 5 "The Promise"
Attended your first trial in the Item World
Killed 100 enemies!
Saw the Axel ending
Completed Ch. 1 "The Overlord's Daughter"