In short:
After you acquire the pink gun, you have to manipulate the tool thief with the shovel in such a way that he ends up being squished on top of the green pyramidz by the rolling boulder.
Detailed information:
First, before you pick up the speed powerup, push him onto the red switch and then back to the center. Then pick up the powerup, step onto the yellow button and push him onto the silver switch as soon as the boulder passes through the two-way arrow.
From there, just make sure that the thief presses the right buttons at the right time so that the boulder doesn't break/drown. If you do it correctly, then the thief should be standing on the red switch as the last button before you will have to push him onto the silver pyramid and then further, to the green pyramidz.
If he does get squished by the boulder as intended, then all you have to do is go to this area and pick up the shovel.

=== Second Section ===
You have to make the green grunt pass through the black switches in the correct order. Pick up the ball and the powerup and just dig up the holes as shown:
When you're done, step onto the green switch, give the green grunt the beach ball and just get to the checkpoint before the toy breaks.

=== Third Section ===
In short:
You have to trick the 3 thieves following you into pressing the purple switches you need. You must use the freezing scrolls to stop them on the switches so that you can go to the area with the arrows and utilize the tools in a correct order. You are going to progressively kill each thief one by one in order to get their tools at the right moment.
Detailed information:
First you need to unlock the 2 trapped thieves by pressing the purple switches at the bottom, first the left one, then the right one.
Then you must go with all of them to the freeze scroll that floats over a hole, in the top left corner. Step onto the switch next to the arrow, wait for them to line up to you, and then just walk onto the arrow. In most cases it should result in them walking onto the switches as intended. Then just use the scroll, go to the area with the arrows, and then fill up the holes and press the switch. Return to the main area.
The rest is done in the same way. Kill the thief with the toob, get the scroll from the water pool, use it and then get across the arrow area to press two switches. Then kill the bricklayer grunt, get the last scroll and then use it to go to the topmost part of the arrow area and press the last switch. Kill the last thief, get his gauntletz and the rest should be obvious.