Here is the full list of all 21 Whipseey and the Lost Atlas achievements.
Defeat 50 enemies.
Swing with the whip.
Jump on an enemy and make it fall into the water.
Hover for at least 3 seconds.
Clear the beach level.
Clear the forest level.
Clear the desert level.
Clear the snow level.
Clear the castle level.
Clear all enemies in any level.
Ride a giant enemy from the snow level.
Clear any level without using a potion.
Clear any level without taking damage.
Clear any level without dying.
Clear a boss without taking damage.
Clear all bosses without taking damage.
Clear beach level boss without dying.
Clear forest level boss without dying.
Clear desert level boss without dying.
Clear snow level boss without dying.
Clear castle level boss without dying.