Here is the full list of all 66 Crystal Story II achievements.
Obtain the Number One Card.
Defeat the Card Master in a card battle.
Defeat the boss of Lao Prison.
Use "Death's Gate" in battle.
Use "Trigger Happy" in battle.
Use "Dragon's Rage" in battle.
Use "Cyclone Dance" in battle.
Defeat the boss of Sunken Ruins.
Complete Chapter VI.
Get a Gold time on Track 3 of Snowboard Extreme!
Defeat Calloc.
Defeat "The Big 3" in the Battle Arena.
Defeat the "Earth, Wind and Fire" in the Battle Arena.
Use "Hurricane" in battle.
Use "Magic Bullet" in battle.
Use "Lucky Strike" in battle.
Use "Dragon's Breath" in battle.
Defeat the "Snowy Chillers" (Hard Mode) in the Battle Arena.
Defeat the "Highlands Flyers" (Hard Mode) in the Battle Arena.
Defeat the "Swamp Stalkers" (Hard Mode) in the Battle Arena.
Win 5 Class GM Card battles.
Defeat the "Desert Crawlers" (Hard Mode) in the Battle Arena.
Catch all the rare fishes.
Defeat the "Small Town Gang" (Hard Mode) in the Battle Arena.
Complete Chapter V.
Complete the Healer tree.
Complete the Trickster tree.
Complete the Guardian tree.
Complete all Wanted Quests
Defeat the "Snowy Chillers" in the Battle Arena.
Complete the Mage tree.
Complete the Thief tree.
Complete the Slayer tree.
Win 5 Class S Card battles.
Win 5 Class A Card battles.
Successfully hack all of the hackable chests.
Defeat all match defense quests.
Defeat the "Royalty" in the Battle Arena.
Defeat the "Highlands Flyers" in the Battle Arena.
Use "Cursed Dagger" in battle.
Win 5 Class B Card battles.
Complete Chapter IV.
Use "Rend" in battle.
Use "Snipe" in battle.
Use "Dragon's Roar" in battle.
Defeat the "Swamp Stalkers" in the Battle Arena.
Complete Chapter III.
Win 5 Class C Card battles.
Defeat "The Dead" in the Battle Arena.
Defeat the "Desert Crawlers" in the Battle Arena.
Complete Chapter II.
Defeat "The Small 3" in the Battle Arena.
Defeat the "Small Town Gang" in the Battle Arena.
Complete Chapter I.
Win 5 Class D Card battles.
Win your first battle.
Defeat the boss of Giant Land.
Defeat the boss of Doom Lair.
Defeat Mechaslime.
Defeat Chimera Prime.
Defeat Foxer.
Defeat Seraph.
Complete the bestiary.
Complete all Wanted X Quests
Win all Mercenary Defense events.
Complete the Secret Quest.