Here is the full list of all 31 Disgaea 1 Complete trophies - there are 16 bronze, 9 silver, 5 gold and 1 platinum.
Obtain all trophies.
Completed Final Episode of Etna Mode "Chronicles of Etnarnia"
Performed 10 transmigrations
Dealt 10,000,000 Damage!
Completed Ep. 1 of Etna Mode "Super Dimensional Etna"
Defeated all EX bosses!
Defeated the Extra Boss "Item God"
Obtained the Hyperdrive!
Defeated the Extra Boss "Item God 2"
Defeated the Extra Boss "Item King"
Defeated the Extra Boss "Baal"
Defeated the Extra Boss "Marjoly"
Obtained Total LV 10,000
Obtained the Dream Hand!
Dealt 100,000 Damage!
Defeated the Extra Boss "Priere"
Obtained Total LV 5,000
Cleared Extra Stages "Cave of Ordeal"
Obtained 10,000,000 HL at the end of battle
Completed Final Episode "What Lies Beyond the Battle"
Obtained 1,000,000 HL
Killed 1,000 enemies!
Completed Ep. 10 "Angels, Demons, and Humans"
Defeated the Extra Boss "Item General"
Killed 500 enemies!
Completed Ep. 5 "Etna's Secret"
Performed your first transmigration
Completed Ep.1 "Prince of the Netherworld".
Killed 100 enemies!
Obtained Total LV 1,000
Obtained Total LV 100