Here is the full list of all 20 Twinsen's Little Big Adventure Classic achievements.
Finish the game
Visit all Islands
Get into the meca-penguin room
Get the magic saber
Give the musician a guitar in Funky Town
Snowboard down the slopes
Become a member of the Elf Club
Find all the Clover Boxes
Retrieve Lanktir’s coffee pot
Fire the canon in the museum
Find the secret passage in the museum
Go on 10 voyages with vehicles
Get the proto-pack
Collect 500 Kashes
Gain the ability to speak to animals
Make the drinking water sweet as syrup
Talk to the Star Wars fanboy
Escape from the prison on Principal or Proxima Island
Acquire the Magic Ball and Magic Tunic
Escape the asylum