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