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