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