World twelve features two normal boxes, five iceboxes and one inert box.
Step by step solution
From the start position - go RIGHT, then go UP and push RIGHT. Go DOWN and push DOWN.
Go LEFT, DOWN, DOWN, RIGHT, RIGHT and push UP. Now go DOWN, LEFT, LEFT, UP, LEFT, LEFT, DOWN and push RIGHT.
Go UP, LEFT, UP, LEFT and push UP. Now go UP, RIGHT, UP, RIGHT and push RIGHT.
Go DOWN, DOWN, DOWN, DOWN, DOWN, LEFT, LEFT, LEFT and push UP. Now go RIGHT, RIGHT, RIGHT, UP, UP, UP, UP, LEFT, LEFT, DOWN and push DOWN.
Go DOWN, DOWN, LEFT, DOWN and push RIGHT.
Go UP, UP, UP, LEFT and push DOWN.
Congratulations. You have completed the twelfth world. Get ready for the thirteenth.