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