Here is the full list of all 16 Legend of Ixtona achievements worth 1,000 gamerscore.
Won 5 battles.
Won 10 battles.
Won 50 battles.
Retreated 10 times.
Dealt the maximum of 3000 damage.
Developed all items not in shops.
Completed all sub-quests.
Sent 5 dispatches.
Sent 10 dispatches.
Sent 50 dispatches.
Hired 10 new characters at the guild.
Got all racial ranks to 10.
Finished the story.
Finished Hard mode or harder.
Finished Chaotic mode.
Defeated Twilight King in Chaotic mode.