Here is the full list of all 21 Whipseey and the Lost Atlas achievements worth 1,000 gamerscore.
Cleared the Castle Level boss without dying.
Cleared all bosses without taking damage.
Cleared the Castle Level.
Cleared the Snow Level boss without dying.
Cleared the Snow Level.
Rode a giant enemy from the Snow Level.
Cleared the Desert Level boss without dying.
Cleared the Desert Level.
Cleared a level without taking damage.
Cleared the Forest Level.
Cleared a level without using a potion.
Cleared the Forest Level boss without dying.
Cleared a boss without taking damage.
Cleared the beach level boss without dying.
Cleared a level with all enemies defeated.
Cleared any level without dying.,
Drowned an enemy.
Cleared the Beach Level.
Hovered for 3 seconds.
Defeated 50 enemies.
Used the whip to swing.