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