Accomplish the indicated achievement to get the corresponding number of Gamerscore points:

Rookie Battler - 10 gamerpoints - Obtain 10% of all battle trophies.
Novice Battler - 10 gamerpoints - Obtain 20% of all battle trophies.
Practiced Battler - 10 gamerpoints - Obtain 30% of all battle trophies.
Skilled Battler - 10 gamerpoints - Obtain 40% of all battle trophies.
Accomplished Battler - 10 gamerpoints - Obtain 50% of all battle trophies.
Seasoned Battler - 10 gamerpoints - Obtain 60% of all battle trophies.
Advanced Battler - 10 gamerpoints - Obtain 70% of all battle trophies.
Expert Battler - 10 gamerpoints - Obtain 80% of all battle trophies.
Master Battler - 10 gamerpoints - Obtain 90% of all battle trophies.
Ultimate Battler - 10 gamerpoints - Obtain 100% of all battle trophies.
Ship Savant - 20 gamerpoints - Collect 100% of all spaceship data.
Arms Addict - 30 gamerpoints - Collect 100% of all weapon data.
Creature Collector - 20 gamerpoints - Collect 50% of all monster data.
Monster Master - 30 gamerpoints - Collect 100% of all monster data.
Dilettante Designer - 20 gamerpoints - Create 20% of all possible items.
Aspiring Architect - 20 gamerpoints - Create 40% of all possible items.
Creative Craftsman - 20 gamerpoints - Create 60% of all possible items.
Inspired Inventor - 20 gamerpoints - Create 80% of all possible items.
World's Biggest Welch Fan - 20 gamerpoints - Create 100% of all possible items.
Treasure Hunter - 20 gamerpoints - Open 50% of all treasure chests.
Treasure Hoarder - 30 gamerpoints - Open 100% of all treasure chests.
Errand Boy - 20 gamerpoints - Complete 30% of all quests.
Potential Postman - 20 gamerpoints - Complete 60% of all quests.
Dutiful Deliverer - 30 gamerpoints - Complete 100% of all quests.

Additionally, there are 26 secret achievements:

Abolished Armaros - 20 gamerpoints - Defeated Armaros on the northern coast of Aeos.
Butchered Barachiel - 20 gamerpoints - Defeated Barachiel in the engine room of the celestial ship.
Squelched Sahariel - 30 gamerpoints - Defeated Sahariel in the Cardianon control tower's central isolation chamber.
Escaped from Earth - 20 gamerpoints - Narrowly escaped from the alternate Earth before its untimely demise...
Trounced Tamiel - 30 gamerpoints - Defeated Tamiel and his Sydonaist henchmen in the hallowed halls of the Purgatorium.
Massacred Manifest - 30 gamerpoints - Defeated Armaros Manifest in the grimy depths of the Miga Insect Warren.
Quelled Kokabiel - 30 gamerpoints - Defeated Kokabiel and her spawn in the sacred En II Sanctuary.
Silenced Satanail - 40 gamerpoints - Defeated Satanail in the Palace of Creation on Nox Obscurus.
Universal Victor - 30 gamerpoints - Completed the game on the Universe difficulty level.
Chaotic Conquerer - 70 gamerpoints - Completed the game on the Chaos difficulty level.
Reimi's Ending - 10 gamerpoints - Viewed Reimi's ending sequence.
Lymle's Ending - 10 gamerpoints - Viewed Lymle's ending sequence.
Bacchus's Ending - 10 gamerpoints - Viewed Bacchus's ending sequence.
Meracle's Ending - 10 gamerpoints - Viewed Meracle's ending sequence.
Myuria's Ending - 10 gamerpoints - Viewed Myuria's ending sequence.
Sarah's Ending - 10 gamerpoints - Viewed Sarah's ending sequence.
Arumat's Ending - 10 gamerpoints - Viewed Arumat's ending sequence.
Faize's Ending - 10 gamerpoints - Viewed Faize's ending sequence.
Crowe's Ending - 10 gamerpoints - Viewed Crowe's ending sequence.
Colosseum Charter - 10 gamerpoints - Broke into the top 30 in solo or team battle rankings.
Colosseum Challenger - 20 gamerpoints - Broke into the top 10 in solo or team battle rankings.
Colosseum Champion - 30 gamerpoints - Took over the top spot in solo or team battle rankings.
Hasty Hare Handler - 10 gamerpoints - Earned 50 victories in class 100 bunny racing.
Rapid Rabbit Wrangler - 20 gamerpoints - Earned 100 victories in class 100 bunny racing.
Celestial Slayer - 40 gamerpoints - Defeated Gabriel Celeste.
Ethereal Executioner - 40 gamerpoints - Defeated the Ethereal Queen.