Level 12: In this one you've got to run across the heads of the enemies
to get the objects from the columns on the left, right at the beginning
of the level.
Level 13: This one requires some tricky timing. Once you've collected all
the objects and are now standing on the enemy's head and he's trapped
inside the yin-yang symbol, dig right to let him out. Drop down and grab
the object where the enemy was. Go right and stand on the enemy's head.
As soon as you can dig the brick on your right. Once that is dug you can
then dig out and release the enemy and the rest is straightforward.