Here is the full list of all 21 Wooden Sen'SeY achievements.
Slice more than 999 enemies
Finish the underwater level without dying
Collect enough SeY to save the village
Finish the boss's whining head
Destroy the boss' ship from underneath
Destroy the boss' ship without touching the ground
Die more than 15 times in one level
Escape the cage
Slice all the enemies in one level
Collect all the SeY bottles in one level
Smash the ground with your axes for the first time
Beat our time in one level
Beat our time in each level
Collect all the SeY bottles in each level
Collect more than 4 000 SeY bottles
Slice all the enemies in each level
Defeat the final boss with bombs only
Earn your first gold medal
Collect all bronze medals
Collect all silver medals
Collect all gold medals