Here is the full list of all 55 Disgaea 2 PC achievements.
Defeated the Extra Boss "Item God"
Defeated the Extra Boss "Mid-Boss"
Completed Ch. 4 of Axel's Story "The Dark Hero!"
Performed your first Peta spell
Reincarnated 10 times
Earned 10,000,000 HL from a single battle
Completed Ch. 1 of Axel's Story "The Evil Rangers"
Performed your first Magichange
Obtained LV 100!
Completed Final Chapter "The Truth"
Defeated the Extra Boss "Prism Ranger"
Completed Ch. 10 "The Two Ninjas"
Killed 1,000 enemies!
Completed Ch. 5 "The Promise"
Obtained 1,000,000 HL!
Unlocked the Dark World
Performed your first reincarnation
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 "Asagi"
Defeated the Extra Boss "Kurtis"
Defeated the Extra Boss "Protype Kurtis"
Defeated the Extra Boss "Priere"
Defeated the Extra Boss "Marjoly"
Defeated the Extra Boss "Flonne"
Defeated the Extra Boss "Laharl"
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 100,000 damage!
Dealt 1,000,000 damage!
Dealt 10,000,000 damage!
Dealt 100,000,000 damage!
Obtained LV 1,000!
Obtained LV 9,999!
Obtained Total LV 5,000
Obtained Total LV 10,000
Obtained the Yoshitsuna!
Unleashed Magichange 2
Saw the Etna ending
Saw the Axel ending
Saw the Laharl ending
Entered the Land of Carnage for the first time
Saw Bad Ending 1
Saw Bad Ending 2
Saw the Tink ending
Obtained 99 felonies