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