The key in the middle is for the door at the top. Move the key left-up-right-right-down.
The bottom key is for the other door. Move the key up-left-up-right-down.
Level 17:
Rotate to push right-moving boxes and down-moving boxes. Start from the button of the right-moving boxes and top of the down-moving boxes.
Level 20: The key at the top is for the door at the top. Move this key first;
The key in the middle is for the door at the middle right. But you need to move the ice block near that key down-right-down first. Then move the key down-right;
They key at the bottom is for the door near the bottom. Move the key to the right and up, use the ice block to put the key in position.
Level 21: Break the ice block with the metal box. The walls won't hurt the ice blocks.
Level 22: The ice blocks are at not for breaking but to forming a path for the green jars. You need to open up all four green squares from the top, then push the ice gems down to the bricks to break the ice and collect the gems.
Level 25: Use the two ice block to put out the fire on the right. Then move the locked box left, then move the key left-up-left to open the box.
Level 27: Move the ? block left and down. Follow the box with the key. Don't let the key touch any door but the one that guards the gems.
Level 34: Pop all the bubbles first. You won't need any to complete this level. You will see the paths clearer once you popped all the bubbles.
Level 36: Use the ice blocks to put the key in the right position.
Levle 41: You don't need all the keys to get the gems. Don't bother with two keys in the upper right area.
Level 42: You need to open the middle door on the top. Move the key first.
Level 45: Three of the four gems are lined up for breaking already. The last one is the tricky one. Remember: Mary Go Around!
Level 49: The metal box is your friend. The TNT will blow up any bricks. The lock boxed can be moved to meet the key.